This allows us to continue execution until a certain proportion of hosts
to fail. This can be useful at scale, where failures are common, and
restarting a deployment is time-consuming.

The default max failure percentage is 100, keeping the default
behaviour. A global max failure percentage may be set via
kolla_max_fail_percentage, and individual services may define a max
failure percentage via <service>_max_fail_percentage.

Note that all hosts in the inventory must be reachable for fact
gathering, even those not included in a --limit.

Closes-Bug: #1833737
Change-Id: I808474a75c0f0e8b539dc0421374b06cea44be4f

Change Ia1239069ccee39416b20959cbabad962c56693cf added support for
running a libvirt daemon on the host, rather than using the nova_libvirt
container. It did not cover migration of existing hosts from using a
container to using a host daemon.

This change adds a kolla-ansible nova-libvirt-cleanup command which may
be used to clean up the nova_libvirt container, volumes and related
items on hosts, once it has been disabled.

The playbook assumes that compute hosts have been emptied of VMs before
it runs. A future extension could support migration of existing VMs, but
this is currently out of scope.

Change-Id: I46854ed7eaf1d5b5e3ccd8531c963427848bdc99