virt: tests: add missing 'display' parameter

This patch brings the recovery functional tests
up-to-date with the last Graphics Device changes
by re-adding the still-mandatory 'display' parameter.

Change-Id: I3d725de480036a0c8b88f03897fba8c16a692fb8
Signed-off-by: Francesco Romani <fromani@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/28587
Reviewed-by: Dan Kenigsberg <danken@redhat.com>