Description of problem:
In 4.2, the matching of the devices reported form libvirt with those defined in the database was moved from vdsm to the engine. But the logic that was introduced for matching the disks is incomplete. It is done according to the 'path' of the disk (like VDSM used to do), but assumes the following logic: the path must contain the disk id. 
However, this logic doesn't hold for LUN disks since their path is composed of "/dev/mapper/<lun_id>". Thus, we need to extend the matching logic for LUN disks, to base on the lun_id instead.

Version-Release number of selected component (if applicable):


How reproducible:
100%

Steps to Reproduce:
1. Run a VM with a plugged LUN disk
2. 
3.

Actual results:
The LUN disk is being unplugged in the engine database

Expected results:
The LUN disk should remain plugged

Additional info:
If the disk is plugged after being unplugged in a previous run of the VM, the VM will start and the LUN disk will remain plugged. So in order to reproduce this bug, we'll need to enforce the devices hash to change by, for example, plugging a NIC.