Add tests for unix_socks_* in libvirtd.conf

Test unix_sock_* parameter in libvird.conf.

1) Change unix_sock_* in libvirtd.conf;
2) Restart libvirt daemon;
3) Check if libvirtd successfully started;
4) Check if libvirtd socket file changed accordingly;

Signed-off-by: Hao Liu <hliu@redhat.com>
redundant return here