Check the createArtifact method

gistfile1.js

(function (server, registry) {

    var log = new Log();

    var GenericArtifactManager = Packages.org.wso2.carbon.governance.api.generic.GenericArtifactManager;
    var GenericArtifactFilter = Packages.org.wso2.carbon.governance.api.generic.GenericArtifactFilter;
    var ByteArrayInputStream = Packages.java.io.ByteArrayInputStream;
    var QName = Packages.javax.xml.namespace.QName;
    var IOUtils = Packages.org.apache.commons.io.IOUtils;

    var buildArtifact = function (manager, artifact) {
  	var data = {
            id: String(artifact.id),
            type: String(manager.type),
			name: String(artifact.getAttribute('overview_name')),
            path: "/_system/governance" + String(artifact.getPath()),
            lifecycle: artifact.getLifecycleName(),
            lifecycleState: artifact.getLifecycleState(),
            mediaType: String(artifact.getMediaType()),
            attributes: (function () {
                var i, name,
                    names = artifact.getAttributeKeys(),
                    length = names.length,
                    attributes = {};
                for (i = 0; i < length; i++) {
                    name = names[i];
                    attributes[name] = String(artifact.getAttribute(name));
                }
                return attributes;
            }())};
		if(artifact.getContent()!=null){
			data.content = function () {
				return new Stream(new ByteArrayInputStream(artifact.getContent()));
            };
		}
        return data;
    };

    var createArtifact = function (manager, options) {
        var name, attribute, i, length, lc,
            artifact = manager.newGovernanceArtifact(new QName(options.name)),
            attributes = options.attributes;
        for (name in attributes) {
            if (attributes.hasOwnProperty(name)) {
                attribute = attributes[name];
                if (attribute instanceof Array) {
                    /*length = attribute.length;
                     for (i = 0; i < length; i++) {
                     artifact.addAttribute(name, attribute[i]);
                     }*/
                    artifact.setAttributes(name, attribute);
                } else {
                    artifact.setAttribute(name, attribute);
                }
            }
        }
        if (options.id) {
            artifact.id = options.id;
        }
        if (options.content) {
                          if (options.content instanceof Stream) {
                              artifact.setContent(IOUtils.toByteArray(options.content.getStream()));
                          } else {
                              artifact.setContent(new java.lang.String(options.content).getBytes());
                          }
                      }
        lc = options.lifecycles;
        if (lc) {
            length = lc.length;
            for (i = 0; i < length; i++) {
                artifact.attachLifecycle(lc[i]);
            }
        }
        return artifact;
    };

    var ArtifactManager = function (registry, type) {
        this.registry = registry;
        var governanceRegistry = Packages.org.wso2.carbon.governance.api.util.GovernanceUtils.getGovernanceUserRegistry(registry.registry, user);
        this.manager = new GenericArtifactManager(governanceRegistry, type);
        this.type = type;
    };
    registry.ArtifactManager = ArtifactManager;

    ArtifactManager.prototype.find = function (fn, paging) {
        var i, length, artifacts,
            artifactz = [];
        artifacts = this.manager.findGenericArtifacts(new GenericArtifactFilter({
            matches: function (artifact) {
                return fn(buildArtifact(this, artifact));
            }
        }));
        length = artifacts.length;
        for (i = 0; i < length; i++) {
            artifactz.push(buildArtifact(this, artifacts[i]));
        }
        return artifactz;
    };

    ArtifactManager.prototype.get = function (id) {
        return buildArtifact(this, this.manager.getGenericArtifact(id));
    };

    ArtifactManager.prototype.count = function () {
        return this.manager.getAllGenericArtifactIds().length;
    };

    ArtifactManager.prototype.list = function (paging) {
        var i,
            artifactz = [],
            artifacts = this.manager.getAllGenericArtifacts(),
            length = artifacts.length;
        for (i = 0; i < length; i++) {
            artifactz.push(buildArtifact(this, artifacts[i]));
        }
        return artifactz;
    };

    /*
     {
     name: 'AndroidApp1',
     attributes: {
     overview_status: "CREATED",
     overview_name: 'AndroidApp1',
     overview_version: '1.0.0',
     overview_url: 'http://overview.com',
     overview_provider: 'admin',
     images_thumbnail: 'http://localhost:9763/portal/gadgets/co2-emission/thumbnail.jpg',
     images_banner: 'http://localhost:9763/portal/gadgets/electric-power/banner.jpg'
     },
     lifecycles : ['lc1', 'lc2'],
     content : '<?xml ....>'
     }
     */
    ArtifactManager.prototype.add = function (options) {
        this.manager.addGenericArtifact(createArtifact(this.manager, options));
    };

    ArtifactManager.prototype.update = function (options) {
		var obj = createArtifact(this.manager, options);
        this.manager.updateGenericArtifact(obj);
    };

    ArtifactManager.prototype.remove = function (id) {
        this.manager.removeGenericArtifact(id);
    };

}(server, registry));

gistfile2.js

	var screenshot1 = files['screenshot1File'];
	screenshot1 = saveFile(screenshot1);

	var screenshot2 = files['screenshot2File'];
	screenshot2 = saveFile(screenshot2);

	var screenshot3 = files['screenshot3File'];
	screenshot3 = saveFile(screenshot3);

	var screenshots = [screenshot1, screenshot2, screenshot3];
	var path = rxtPath + ctx.provider + '/' +ctx.name+ '/' +ctx.version;
	
	if(ctx.packagename == undefined ||ctx.packagename == ""){
		ctx.packagename = "com.wso2mobile.wso2phonedirectory";
	}
	// Packages.org.wso2.carbon.governance.api.util.GovernanceUtils.loadGovernanceArtifacts(registry.registry);
	am = new carbon.registry.ArtifactManager(registry, "mobileapp");
	var attributes ={
        overview_status: "PENDING-REVIEW",
        overview_name: ctx.name,
		overview_platform:t,
        overview_version: ctx.version,
        overview_url: ctx.url,
        overview_provider: ctx.provider,
		overview_description: ctx.description,
		overview_market:ctx.markettype,
		// overview_recentChanges:ctx.recentChanges,
		overview_packageName:ctx.packagename,
		overview_category:ctx.category,
		images_icon:icon,
		images_banner:banner,
		images_screenshots:screenshots //Culprit
    };
	attributes[attributes.overview_status+"_date"]=printDate();
	am.add({
		    name: ctx.name,
			lifecycle:["applifecycle"],
			path:path,
			attributes:attributes 
		});

gistfile3.xml

<screenshots>one</screenshots>
<screenshots>two</screenshots>
<screenshots>three</screenshots>