Add support for epel-testing through variable REPOSITORY_EPEL_TESTING_ENABLED
(disabled by default)
Allow both epel and os-based (e.g. sl6_epel) repository template to be used
(same for epel-testing)
Merge pull request #44 from jouvin/sl6.x-epel-testing

Add support for epel-testing through variable REPOSITORY_EPEL_TESTING_ENABLED