Add compatibility for rspec-puppet 0.2.0

As per rodjek/rspec-puppet#56 the puppetlabs_spec_helper and rspec-puppet test initialization is mixed and conflated thus causing cyclic gem dependencies. In rodjek/rspec-puppet@41257b3 parts of the `Puppet::Test::TestHelper` initialization code has been included in the rspec-puppet project. This code should be removed from puppetlabs_spec_helper to avoid incompatibilities with rspec-puppet 0.2.0 upon release.