qemu-iotests: Test automatic commit job cancel on hot unplug

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>
(cherry picked from commit c3971b88)
*prereq for d3c8c674
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>