We're more likely to time out while waiting for the
action's result if we launch an action while the
model is still executing. Thus it's safer to wait
for the model to settle between actions.
This patch modifies the existing openstack upgrade tests so that they
work with focal (by explicitly supporting mysql-innodb-cluster), and are
also interruptable and resumable (at a charm level). It also makes them
work with the udpated 'get_upgrade_groups()' that ultimately gets a List
of Tuples rather than a dictionary.
