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"
xenapi: post install scriptlet to rpm

A freshly installed XenServer requires some modifications in order to be
able to run OpenStack. Nova contains an rpm specification to create a
package with the dom0 plugins, however installing the rpm is not enough.
Some more actions need to be taken:
 - create /images, link to a directory within the local SR
 - setup an ssh keypair, and authenticate it with the host
This change adds a post script to the nova plugins rpm spec file, so
by installing the rpm on a XenServer, it is ready to run OpenStack, no
further manual actions needed.

Change-Id: Id57e3a3ab2782550468c6aa4c01059ceb7cc81ab