In some cases it may be desirable to run the libvirt daemon on the host.
For example, when mixing host and container OS distributions or
versions.

This change makes it possible to disable the nova_libvirt container, by
setting enable_nova_libvirt_container to false. The default values of
some Docker mounts and other paths have been updated to point to default
host directories rather than Docker volumes when using a host libvirt
daemon.

This change does not handle migration of existing systems from using
a nova_libvirt container to libvirt on the host.

Depends-On: https://review.opendev.org/c/openstack/ansible-collection-kolla/+/830504

Change-Id: Ia1239069ccee39416b20959cbabad962c56693cf