Add test for option libvirtd_config in sysconfig file

Test libvirtd_config parameter in /etc/sysconfig/libvirtd.

1) Change libvirtd_config in sysconfig;
2) Change host_uuid in newly defined libvirtd.conf file;
3) Restart libvirt daemon;
4) Check if libvirtd successfully started;
5) Check if host_uuid updated accordingly;

Signed-off-by: Hao Liu <hliu@redhat.com>
error.TestFail also not support implicit substitution.