wait_for_login() related update

Redhat ID: 1080834



@FengYang Hi test it. but find some problem here. The login here is just behind the dhclient cmd is sent to guest. It is impossible for guest to get ip here. So it still will failed with "No ipv4 DHCP lease for MAC 9a:a5:a6:a7:a8:a9". Can we add some method to let the network restart command can return then we try to login again?