vdsm: fix Vm cleanup routine

The issue was that on Vm disk hot unplug the general clean up routine
was called, that wiped out also qemu and ovirt guest agent's sockets.

Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=927143
Signed-off-by: Peter V. Saveliev <peet@redhat.com>
Change-Id: Ie355022866d008a83257b1b6e3a4226a07d34c2f
Reviewed-on: http://gerrit.ovirt.org/13610
Reviewed-by: Dan Kenigsberg <danken@redhat.com>
Reviewed-by: Vered Volansky <vvolansk@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/15055
Tested-by: Federico Simoncelli <fsimonce@redhat.com>