vdsm: Fix diskReplicateFinish call description

vdsClient diskReplicateFinish had the same description as Start.
Changed "Start" to "Finish".

Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=901606
Change-Id: I5b644540c5845d7377f50c379460c8ab5868ee9b
Signed-off-by: Vered Volansky <vvolansk@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/11377
Reviewed-by: Allon Mureinik <amureini@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>