Description of problem:
The PopulateDirectLUNDiskDescriptionWithLUNId key of engine config:
"When creating direct LUN disk the number of characters from LUN id to populate the description with (-1 = the full id, 0 = none, >0 = number of characters)" (Value Type: Integer)

When creating the direct LUN disk from REST API, this functionality is not working


Version-Release number of selected component (if applicable):
vdsm-4.17.19-0.el7ev.noarch
rhevm-3.6.2.6-0.1.el6.noarch

How reproducible:
100%

Steps to Reproduce:
1. engine-config -s PopulateDirectLUNDiskDescriptionWithLUNId=-1 # (For full ID)
2. Restart ovirt-engine service
3. Create direct LUN disk using REST API:
POST https://<fqdn>/api/disks 

<disk>
    <alias>direct_lun_test</alias>
    <size>1073741824</size>
    <interface>virtio_scsi</interface>
    <format>cow</format>
    <bootable>false</bootable>
    <lun_storage>
        <type>iscsi</type>
        <logical_unit id="<LUN_ID>">
            <port>3260</port>
            <target><IQN></target>
            <address><IP></address>
        </logical_unit>
    </lun_storage>
</disk>

Actual results:


Expected results:


Additional info: