Updating the environment used by the update hook to rbenv ruby

It appears that the "update" hook from gitlab-shell defaults to
system ruby, raising errors on mismatched versions for rake when
trying to edit files using the web interface.
Forcing it to use rbenv ruby solves the issue.
Adding spec tests for update hook template
gemfile: Unpin rspec and puppet-lint gems
Convert specs to RSpec 2.99.2 syntax with Transpec
(qa) Fix lint issue due to puppet-lint 1.0.1 upgrade
Merge pull request #191 from sbadia/qa-rspec

Qa rspec
Merge pull request #186 from frconil/rbenv_update_hook_fix

Updating the environment used by the update hook to rbenv ruby
(spec) Initial rspec-beaker testing scaffolding

This allows basic beaker testing to be performed inside the beaker
testing framework. (thanks @nibalizer)!

Closes: #20
(spec) remove unused rspec-system files

(we use now acceptance and beaker)

Refs: #20
(cherry picked from commit 275901ac9b720a844d931bea9ea5f53937bca5ca)