Enables the user to specify the group of /home/user/.rbenv.

jenkins package will add jenkins user
and the owner and group of jenkins home directory is: jenkins and nogroup.

Before this commit,
this cookbook assumes that the owner and group
of /path/to/.rbenv is the specified user.
For example, if you install Ruby under kazu634's home directory,
its .rbenv directory owner and group owner is: kazu634:kazu634.

This will not work for jenkins case.

After this commit,
you can specify the owner and group owner of /home/user/.rbenv separately.

This commit refs #198.
Modify README.md to illustrate how to use this cookbook.

This commit fixes #198.
Delete virtualbox cookbook.

Jenkins now use docker to test Chef's recipe,
so the virtualbox will no longer be used.

This commit refs #194.
Add jenkins::docker recipe to install docker.

jenkins will use docker to test Chef's recipes,
so that jenkins::docker recipe will install docker.

Internally, jenkins::docker will call docker cookbook.

This commit refs #194.
Install Ruby under jenkins user's home directory.

jenkins will use Ruby to test Chef's recipe,
so that Ruby should be available when jenkins provides its service.

This commit refs #194.
SSH configuration

  - Deploy the SSH-related files.
  - Add the task of jenkins SSH key generation.

This commit fixes #194.
Merge branch 'id/194' into dev