openstack-common: Fixing epel repository call

I was using the chroot directory instead of the DIST name... the EPEL
repo wasn't setup at all.
packages: Adding add_satellite_repository()

When SATELLITE_USERNAME and SATELLITE_PASSWORD variables are set, when
running a Redhat OS, the Redhat Network Satellite is configured to get
updates and additional packages.

i.e : puppet package requires rubygems which is only available on the
optional repository.

This patch configure the RHN regarding the user & password given.

Note it requires the "System Group Administrators and Satellite
Administrators" to give the proper rights to SATELLITE_USERNAME.