libvirt: support SASL authentication

Adds support for SASL authentication of libvirt TCP and TLS connections
when using a compute host libvirt daemon.

In line with the dependent Kolla Ansible patch, we enable SASL by
default, and use DIGEST-MD5 with TCP and SCRAM-SHA-256 with TLS.

Depends-On: https://review.opendev.org/c/openstack/kolla-ansible/+/833022
Depends-On: https://github.com/stackhpc/ansible-role-libvirt-host/pull/52

Story: 2009858
Task: 44735

Change-Id: Id3972c24022aeb6421494c3cccdc8e7cbce802e6