qdev-monitor: Set properties after parent is assigned in device_add

Test steps:
 (qemu) device_add e1000,addr=adsf
  Property 'e1000.addr' doesn't take value 'adsf'
 (qemu) info qtree
  Then qemu crashed.

Currently we set a link to the new device from its parent bus, but the
device hasn't been added to QOM tree yet. When it fails to set properties,
object_unparent() can't clean up the device.

Delay setting of device properties until the device has been added to
the QOM composition tree. This way, when setting a property fails,
object_unparent() can clean up the device properly.

Signed-off-by: Amos Kong <akong@redhat.com>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>
