Add QEMU driver support for job info on migration ops

Add QEMU driver support for job info on migration ops

Introduce support for  virDomainGetJobInfo in the QEMU driver. This
allows for monitoring of any API that uses the 'info migrate' monitor
command. ie virDomainMigrate, virDomainSave and virDomainCoreDump

Unfortunately QEMU does not provide a way to monitor incoming migration
so we can't wire up virDomainRestore yet.

The virsh tool gets a new command 'domjobinfo' to query status

* src/qemu/qemu_driver.c: Record virDomainJobInfo and start time
  in qemuDomainObjPrivatePtr objects. Add generic shared handler
  for calling 'info migrate' with all migration based APIs.
* src/qemu/qemu_monitor_text.c: Fix parsing of 'info migration' reply
* tools/virsh.c: add new 'domjobinfo' command to query progress