(maint) Add Beaker to :system_tests gem group
(maint) Add Beaker to :system_tests gem group

 - Without Beaker in isolation, there is no way to actually install
   the bundle for this module on Windows, since Beaker contains gems
   with native extensions that don't compile on Ruby 2.1.5 and Windows
   (unf_ext in particular).

   With this change, we can now install the gems to be used for
   local integration testing with:

   bundle install --path .bundle/gems --without=system_tests

zshahan/puppetlabs-registry,jpogran/puppetlabs-registry,ferventcoder/puppetlabs-registry,DSI-Ville-Noumea/puppetlabs-registry,cyberious/puppetlabs-registry,MelanieGault/puppetlabs-registry,puppetlabs/puppetlabs-registry