Fix DevStack Ceph on the Giant release

As of the Ceph Giant release, pools 'data' and 'metadata' (used for
CephFS) were removed. Thus applying the pool change command fails on
Giant since those pools don't exist anymore. Now we are checking for
every release prior to Giant and apply proper commands accordingly.

Change-Id: Ia12042899c0e6809f5b98c2e0de177bb61c8a790
Signed-off-by: Sébastien Han <sebastien.han@enovance.com>
Merge "Fix DevStack Ceph on the Giant release"
Merge branch 'master' of https://github.com/openstack-dev/devstack