Add leader election for periodic sync with ironic

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

ironic_inspector/conf/default.py

@@ -64,6 +64,9 @@ _OPTS = [
                       'Not advisable if the deployment uses a PXE filter, '
                       'and will result in the ironic-inspector ceasing '
                       'periodic cleanup activities.')),
+    cfg.IntOpt('leader_election_interval',
+               default=10,
+               help=_('Interval (in seconds) between leader elections.')),
     cfg.BoolOpt('use_ssl',
                 default=False,
                 help=_('SSL Enabled/Disabled')),