To avoid inconsistency between the fqdn added to the nova.conf
'host' config and the hostname set of the cloud-compute relation
we need to ensure that both are using the same means of determining
the host fqdn. This is so that the when nova-cloud-controller
charm populates ssh known_hosts and shares with all computes it
definitely contains an entry for the nova.conf host config since
this is sometimes used as part of a live-migration.
Change-Id: Iddcf3fdacf7e7374b57b628edf1e6d0df4da082c
Closes-Bug: #2089781