Description of problem:
after updating a vm twice with different payloads through RESTapi, vm fails to start.

Version-Release number of selected component (if applicable):
is12

Steps to Reproduce:

1. Create Vm and install RHEL 6.4
2. Stop vm and create template
3. create 5 vms pool from template.
4. with the RESTapi update one vm from the pool with payload:

PUT .../api/vms/da37a39c-807b-4150-b369-a8698a696acb/

<vm>
<payloads>
<payload type="cdrom">
<file name="file1.update.cdrom">
<content>'some content cdrom 1!'</content>
</file>
</payload>
</payloads>
</vm>

5. start vm.
6. ssh vm and run command: mkdir /tmp/cdrom_payload1; mount /dev/cdrom1 /tmp/cdrom_payload1;
7. file.update.cdrom should be vissibl with its content in folder /tmp/cdrom_payload1.
8. umount /dev/cdrom1
9. check that file doesn't exit anymore.
10. stop vm
11. with the RESTapi update the same vm with a new payload:

PUT .../api/vms/da37a39c-807b-4150-b369-a8698a696acb/

<vm>
<payloads>
<payload type="cdrom">
<file name="file2.update.cdrom">
<content>'some content cdrom 2!'</content>
</file>
</payload>
</payloads>
</vm>

12. start vm in order to reproduce the same procedure.


Actual results:

vm fails to start, both from GUI and RESTapi.

Expected results:

vm should start and new payload should be available for mounting as prior payload.

Additional info:

logs attached