With multi-cell support in Pike, we should deprecate cells v1
so we can at least start the deprecation signaling in the
docs and release notes. We may not end up removing cells v1
code in Queens, but this at least gives us the option.
Note that we also want to do this because nova-network cannot
be removed until we remove cells v1.
Change-Id: I1a173f7ce0715e684850e030c358e8175fa8724c