virt: Fix some problem in qemu-devices for unplug of devices.

Adds verification of unplug operation based on info qtree.

rename hotplug and unplug to simple-hotplug and simple-unplug

Change behavior of DevContainer hot-unplug and hot-plug:
old:
 1) remove/insert object from/to DevContainer
 2) try to remove/insert object from/to VM
 problem) if removing from VM failed it there is no reasonable way how
                 call unplug funtion again.
new:
 1) try to remove/insert or insert dev from VM
 if-succ) remove/insert object from DevContainer.
 it allows repeatbly remove dev from DevContainer.

Signed-off-by: Jiří Župka <jzupka@redhat.com>
virt: Adds multihost hot-plug and hot-unplug block dev tests.

steps:
  1) start VM
  2) hot-plug hot-unplug block dev
  3) migrate
  4) check VM

conf:
  only (multihost_mig_tests=hotplug_disk_test).hotplug
  only (multihost_mig_tests=hotplug_disk_test).unplug

Signed-off-by: Jiří Župka <jzupka@redhat.com>
virt: Changes Multihost control file.

Signed-off-by: Jiří Župka <jzupka@redhat.com>