Add quality warning for non-standard libvirt configurations

This adds a warning log message to the administrators about libvirt
driver configurations that are not tested upstream. Things like
libvirt-lxc, libvirt-uml, and non-intel KVM architectures are the
primary target of this warning.

Change-Id: I17ee1e3c07510382254f45d99f557b227ac8470c
Merge "Add quality warning for non-standard libvirt configurations"