(maint) No longer necessary to gem install rgen

Puppet used to express gem dependencies on rgen in its Gemfile, packaging,
etc, but in PUP-2914 the rgen code was vendored into puppet, and the
dependencies removed.

However, the future parser setup step still tried to install the rgen
gem, but only when testing against git checkouts (effectively Solaris
and Windows).

Since rgen is vendored in puppet, it is not necessary to install the gem
during future parser testing.
Merge pull request #3365 from joshcooper/maint/stable/remove-rgen-install

(maint) No longer necessary to gem install rgen
(maint,QENG-174) Allow installing a new puppet package on top of the PE tar

Currently, when running the puppet acceptance tests against PE, you
can only test the version of puppet that is shipped with the PE
tarball. This adds another step to the PE pre-suite which will install
an arbitrary version of pe-puppet on top of the installed PE tarball.
Merge pull request #3366 from branan/QENG-174

(maint,QENG-174) Allow installing a new puppet package on top of the PE tar
Merge branch 'stable'

* stable:
  (maint,QENG-174) Allow installing a new puppet package on top of the PE tar
  (maint) No longer necessary to gem install rgen

Conflicts:
	acceptance/setup/common/pre-suite/100_SetParser.rb

This was removed in master prior to the change in stable. It was only
used to distinguish between current/future parser runs, and that
distinction no longer exists post PUP-3274, so it remains removed in
master after this merge.