Fix VDSM boot

Fix regression introduced in Gerrit 22750, hash 114692f.

The unified net persistence upgrade name was changed, changing
the name exposed to vdsm-tool. However, the call to the upgrade
was still using the old name.

Change-Id: Iaa0fadae424e93b43cafc2b1519f59e88e7c5832
Signed-off-by: Assaf Muller <amuller@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/23218
Reviewed-by: Piotr Kliczewski <piotr.kliczewski@gmail.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>