Split $RHOS logic into a $RHOS and $RHOS_RELEASE. Will allow us to disable use of epel/rdo, and make rhos-release optional.
Split $RHOS logic into a $RHOS and $RHOS_RELEASE. Will allow us to disable use
of epel/rdo, and make rhos-release optional.

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