Description of problem:

Before plugging external luns to vms, we setup up a temporary udev rule
for setting device permissions. Using this rule will cause the device to
loose the libvirt selinux label if a device has a change event, and 
running with recent systemd-udevd (e.g. Fedora 19 and later, EL 7).

This is the same issue we had with vdsm images, (bug 1127460) but with
external luns we do not trigger change events, so the issue is unlikely.
However, if it happens, it will cause a vm to pause.

Version-Release number of selected component (if applicable):
vdsm master Oct 10.

How reproducible:
Always

Steps to Reproduce:
1. Start a vm using an external lun for one of the disks
2. Trigger a change event on a device used as external lun
   udevadm trigger --verbose --action change \
      --property-match=DM_NAME=1IET_0006000a

You need to replace 1IET_0006000a with the actual device name, can be
found using multipath -ll.

Actual results:
The device will loose the svirt_image_t:s0:cxxx,cyyy label, and will get the default label fixed_disk_device_t:s0 intead. This will cause the vm to pause.

Expected results:
Libvirt sexlinux label kept and vm keep running.