Katello SCL for RHEL6

This adds SCL support for RHEL6. So on RHEL6 we are now using SCL, on Fedora we are runnning against standard Ruby and Gems.

Note I have disabled two things:

 * apipie - @inecas can you take a look once you have time (there is some error there)
 * gettext mo generation - we do not use MO files at all and it required additional build deps which are not necessary

I want to go ahead and implement gettext generation in the same way we use in katello-utils using plain GNU gettext. Will be faster and without need of rubygem-gettext for the build time.

This will be enabled in the next nightly, I also need to put several new deps into the compose files.

http://koji.katello.org/koji/taskinfo?taskID=26860

http://koji.katello.org/koji/taskinfo?taskID=26862