Description of problem:

During the hotplug, the engine does pass the reservations param to the host.

~~~
2021-12-02 17:59:47,596+05 INFO  [org.ovirt.engine.core.vdsbroker.vdsbroker.HotPlugDiskVDSCommand] (default task-6) [3cda65f7] START, HotPlugDiskVDSCommand(HostName = dell-r530-4.gsslab.pnq.redhat.com, HotPlugDiskVDSParameters:{hostId='213ae779-00b1-4a7c-abce-f8f5c116b7bf', vmId='9af0a1ea-18df-4d94-95dc-41b28c088ced', diskId='11dd18bc-9977-4a48-8a00-8afe133634e8'}), log id: 7332387e
2021-12-02 17:59:47,598+05 INFO  [org.ovirt.engine.core.vdsbroker.vdsbroker.HotPlugDiskVDSCommand] (default task-6) [3cda65f7] Disk hot-plug: <?xml version="1.0" encoding="UTF-8"?><hotplug>
  <devices>
    <disk snapshot="no" type="block" device="lun" sgio="unfiltered">
      <target dev="sda" bus="scsi"/>
      <source dev="/dev/mapper/360014050cb6f143b0cd4bd19dc461994">
        <reservations managed="yes"/>                                <<<<<<<<<<<<
        <seclabel model="dac" type="none" relabel="no"/>
      </source>
      <driver name="qemu" io="native" type="raw" error_policy="stop" cache="none"/>
      <alias name="ua-11dd18bc-9977-4a48-8a00-8afe133634e8"/>
      <address bus="0" controller="0" unit="1" type="drive" target="0"/>
    </disk>
  </devices>

~~~

I can see the same on the hotplug vdsm API.

~~~
2021-12-02 17:59:47,605+0530 INFO  (jsonrpc/1) [api.virt] START hotplugDisk(params={'vmId': '9af0a1ea-18df-4d94-95dc-41b28c088ced', 'xml': '<?xml version="1.0" encoding="UTF-8"?><hotplug><devices><disk snapshot="no" type="block" device="lun" sgio="unfiltered"><target dev="sda" bus="scsi"></target><source dev="/dev/mapper/360014050cb6f143b0cd4bd19dc461994"><reservations managed="yes"></reservations>...... vmId=9af0a1ea-18df-4d94-95dc-41b28c088ced (api:48)
~~~

But not in the xml which it is sending to libvirtd.

~~~
2021-12-02 17:59:48,715+0530 INFO  (jsonrpc/1) [virt.vm] (vmId='9af0a1ea-18df-4d94-95dc-41b28c088ced') Hotplug disk xml: <?xml version='1.0' encoding='utf-8'?>
<disk device="lun" sgio="unfiltered" snapshot="no" type="block">
    <address bus="0" controller="0" target="0" type="drive" unit="1" />
    <source dev="/dev/mapper/360014050cb6f143b0cd4bd19dc461994">
        <seclabel model="dac" relabel="no" type="none" />
    </source>
    <target bus="scsi" dev="sdb" />
    <driver cache="none" error_policy="stop" io="native" name="qemu" type="raw" />
    <alias name="ua-11dd18bc-9977-4a48-8a00-8afe133634e8" />
</disk>
 (vm:3851)
~~~

Looks like the "reservations" is silently getting dropped at "diskParams = storagexml.parse(elem, meta)". So the disk is created without "reservations" param and hence the `qemu-pr-helper` process will not get generated.

~~~
virsh -r dumpxml vmname |grep -A 9 -i sgio
    <disk type='block' device='lun' sgio='unfiltered' snapshot='no'>
      <driver name='qemu' type='raw' cache='none' error_policy='stop' io='native'/>
      <source dev='/dev/mapper/360014050cb6f143b0cd4bd19dc461994' index='3'>
        <seclabel model='dac' relabel='no'/>
      </source>
      <backingStore/>
      <target dev='sdb' bus='scsi'/>
      <alias name='ua-11dd18bc-9977-4a48-8a00-8afe133634e8'/>
      <address type='drive' controller='0' bus='0' target='0' unit='1'/>
    </disk>
~~


The user has to stop and start the VM for the reservations to work. 

After stop and start of the VM.
~~~
virsh -r dumpxml kubevirt |grep -A 9 -i sgio
    <disk type='block' device='lun' sgio='unfiltered' snapshot='no'>
      <driver name='qemu' type='raw' cache='none' error_policy='stop' io='native'/>
      <source dev='/dev/mapper/360014050cb6f143b0cd4bd19dc461994' index='1'>
        <seclabel model='dac' relabel='no'/>
        <reservations managed='yes'>                        <<<<<<<<<<<<<<<<<<<<
          <source type='unix' path='/var/lib/libvirt/qemu/domain-3-kubevirt/pr-helper0.sock' mode='client'/>
        </reservations>
      </source>
      <backingStore/>
      <target dev='sdb' bus='scsi'/>
~~~


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

vdsm-4.40.90.4-1.el8ev.x86_64

How reproducible:

100%

Steps to Reproduce:

1. Create and start a VM.
2. Hotplug a direct LUN disk by checking "Using SCSI Reservation".
3. Check in the VMs XML if reservations parameters are added in XML.

~~~
virsh -r dumpxml vm-name
~~~

4. Also, there will not be "qemu-pr-helper" process created for the VM.


Actual results:

SCSI reservation is not working for hot plugged VM disks.