[libvirt] qemu: Add timeout for monitor to avoid virsh getting stuck when monitor gets die.

Hello Guys, When the qemu process becomes hung, virsh will get stuck on the hung guest and can't move forward. It can be reproduced by the following steps: 1. setup a virt guest with qemu-kvm, and start it 2. stop qemu process with following: kill -STOP `ps aux | grep qemu | grep -v grep | awk '{print $2}'` 3. run the following command: virsh list I think we can add a timeout for qemu monitor to resolve this problem: using virCondWaitUntil instead of virCondWait in qemuMonitorSend. What's your opinions? Thanks!