Periodically elect a leader to do the cleanup sync with
Ironic (to avoid unnecessary calls to Ironic in a
multi-inspector setup).
Add config option 'leader_election_interval' to control
the period in which the leaders is elected.
Co-authored-by: Arne Wiebalck <arne.wiebalck@cern.ch>
Story: #2007801
Change-Id: I6f60aea41865f09f9e53e5d91b1e887f0b39efbd