This patch aim to update our specs test in order to work with the new
rspec-puppet release 2.0.0, in the mean time, we update rspec syntax
in order to be prepared for rspec 3.x move.
* Use shared_examples "a Puppet::Error" for puppet::error tests
* Convert 'should' keyword to 'is_expected.to' (prepare rspec 3.x)
* Fix spec tests for rspec-puppet 2.0.0
* Upgrade and pin rspec-puppet from 1.0.1 to 2.0.0
* Clean Gemfile (remove over-specificication of runtime deps of puppetlabs_spec_helper)