gistfile1.gradle

project.ext.versionCode = project.hasProperty("versionCode") ? project.versionCode.toInteger() : 3
project.ext.versionName = project.hasProperty("versionName") ? project.versionName : "1.0"

android {
    defaultConfig {
        versionCode project.versionCode
        versionName project.versionName
    }
    applicationVariants.all { variant ->
        variant.outputs.each { output ->
            output.outputFile = new File(output.outputFile.parent, 
              output.outputFile.name.replace("app-debug.apk", 
              "MyApp_" + "_v" + project.versionName + "." + project.versionCode + ".apk"))
        }
    }
}