Currently whenever the shared-db hook fires we call
migrate_neutron_database() which will always (unless unit
is paused) do a migration and restart the neutron-server
service. This is unnecessary and disruptive so we avoid
doing this by first checking whether we have already
initialised and and skipping migrate and restart if we
have already initialised. We also add support to override
this logic if an upgrade is in progress.
Change-Id: Ia4c104ff21d10a0d24ac3038bb75a5a9dc67ca94
Closes-Bug: 1708459
2c21ad14ab