Update version aliases for rpc version control

Now that Havana has been branched, add aliases for the rpc version
implemented by Havana.  These aliases can be used in the configuration
options for doing outbound rpc version control.

This is one of the items that should be done after every release, and
has been added to the new release checklist wiki page:

    https://wiki.openstack.org/wiki/Nova/ReleaseChecklist

DocImpact - 'havana' is now a valid value to provide to all of the
options in the [upgrade_levels] section of nova.conf.

Change-Id: Ifa0b3dcc00843ad3f045a450ceb0f47f0b843f98
Merge "Update version aliases for rpc version control"