libvirt.conf: Add test for host_uuid option

Test host_uuid parameter in libvird.conf.

1) Change host_uuid in libvirtd.conf;
2) Restart libvirt daemon;
3) Check if libvirtd successfully started;
4) Check current host UUID by `virsh capabilities`;

Signed-off-by: Hao Liu <hliu@redhat.com>
Merge pull request #252 from Hao-Liu/host_uuid

libvirt.conf: Add test for host_uuid option