openstack: avoid rhel-x86_64-server-6-ost-4 channel

rhel-x86_64-server-6-ost-4 channel is not available so far. With this
changes we use instead:
 - rhel-x86_64-server-sfs-6
 - rhel-x86_64-server-6-ost-4
 - a local mirror of rhel-x86_64-server-6-ost-4
o-full: only use the minimal ceph repo

we don't need extra ceph packages so far. let's avoid conflict with
RHEL base system.
o-full: do not disable puppet and epel

why these repositories should be removed?