[libvirt] Tunnelled migration

[Chris Lalancette]

At long last, now that the stream stuff is committed to the tree,
I can repost the tunnelled migration patches.  Note that these
patches will conflict in some places with danpb's previously
posted "PEER2PEER" patches, but it should be easy to
resolve the differences.

V2: Rework the monitor patch to be an API
    Use the new monitor API
    Remove silly use of qemuEscapeMonitorArgs()