Always install yum-plugin-priorities
Always install yum-plugin-priorities

This was only being installed for RHEL with rhos-release.  We
actually need it everywhere, so the install needs to be moved out
of the RHEL/rhos-release conditional.

Change-Id: I6d0d5d177a82c40fc69ad5171ca7bdee89613a56

dmsimard/instack-undercloud,bcrochet/instack-undercloud,rdo-management/instack-undercloud,eprasad/instack-undercloud,eprasad/instack-undercloud,dpkshetty/instack-undercloud,rdo-management/instack-undercloud,dmsimard/instack-undercloud,dpkshetty/instack-undercloud,bcrochet/instack-undercloud