Ruby module for better management of ruby and gems

Implemented a ruby module that provides resources for ensuring the
installation of specific and isolated versions of ruby, gems, and
gemsets. Different rubies and their gems are installed to isolated
environments using rbenv. Gemsets are handled by bundler and, by
default, isolated under project directories.

Use of specific versions of Ruby when executing commands can be
enforced on a directory or user level using the respective
ruby::version resource.

Documentation and examples are provided inline for each puppet manifest.

Modified browsertests role to use new ruby module.

Bug: 50993
Change-Id: Ia3edc2a79e54b412a00564740832b3adaad3ec92
Merge "Ruby module for better management of ruby and gems"