(maint) Have Beaker add epel repo for rhel platforms during acceptance

Epel repo has been removed from our vcloud templates, but when testing
hiera from git source checkout, we need to be able to install git first,
and rhel5/centos5 does not have this package without epel enabled.  We
can remove this flag when we are no longer testing on rhel5, or no
longer need git (solely testing from packages).
Merge branch 'maint/stable/include-epel-for-acceptance' into stable

* maint/stable/include-epel-for-acceptance:
  (maint) Have Beaker add epel repo for rhel platforms during acceptance