@ypu 
Hi, I am updating this branch.
But, hmm...do you really mind I add this method in virt_vm.py so much?
Yes, maybe you believe it is useless for qemu vm, but I think a functionality to update mac address is 
usefull for anytype vm.

What's worse, I tried to make it private for libvirt_vm and call it in wait_for_get_address.
But It looks so bad. Calling a method of subclass make me upset. It breaks the DIP(Dependency-Inversion Principle)
obviously.

So, my suggestion is add this method into virt_vm, and wait for implement for qemu.

Do you aggree?