Drop remnant CMD_LOWPRIO

Commit aba12f81be549 attempted to drop all CMD_LOWPRIO, but due to a sloppy
rebase, one reference remains.

Change-Id: I9f361a0de7a928cc7207221144d0a2b5396f413c
Signed-off-by: Dan Kenigsberg <danken@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/12184
Reviewed-by: Saggi Mizrahi <smizrahi@redhat.com>