Do not call `virsh` in libvirt hooks

[zhiyuanzhai]

According to the document of libvirt:

Calling libvirt functions from within a hook script
DO NOT DO THIS!
A hook script must not call back into libvirt, as the libvirt daemon is already waiting for the script to exit.
A deadlock is likely to occur.

Maybe we should use other CLI tools like sysfs instead.