Wercker上でprivateリポジトリのsubmodule ref: http://qiita.com/koizuss@github/items/8aed954bd10a8e64fca8

file0.yml

build:
  steps:
    # ...
    #  `git` `openssh-client` がないboxの場合は事前にインストール
    - script:
        name: package install
        code: |
          yum install -y git openssh-client
    # see http://devcenter.wercker.com/docs/git/submodules
    - add-ssh-key:
        keyname: BITBUCKET_KEY
        host: bitbucket.org
    # see https://github.com/wercker/step-add-to-known_hosts
    - add-to-known_hosts:
        hostname: bitbucket.org
        fingerprint: 97:8c:1b:f2:6f:14:6b:5c:3b:ec:aa:46:46:74:7c:40
        type: rsa
    - script:
        name: git submodule
        code: |
          git submodule update --init