Add wait_for_agent_status in 'settle' code

This is to guarantee that the block check didn't happen prior to the
action being started.

zaza/openstack/charm_tests/mysql/tests.py

@@ -642,6 +642,7 @@ class MySQLInnoDBClusterRotatePasswordTests(MySQLCommonTests):
 
         # let everything settle.
         logging.info("Waiting for model to settle.")
+        zaza.model.wait_for_agent_status()
         zaza.model.block_until_all_units_idle()
 
         # verify that the password has changed.