Ceph is pretty easy to work with. Upgrade mons, then osds, then rgws
We want to eventually make these serial values configurable, but for
now due to cephs delicate distributed network nature it is safest to
only run 1 change at a time.
Change-Id: Icc721ab3651379c28fee853ca95f9e3ddf102998
Partially-Implements: blueprint upgrade-kolla
Implements: blueprint upgrade-ceph