Updated openstack/openstack
Project: openstack-infra/devstack-gate  3c4e0bd294ed22c9d41379c23adae78b3f10d676

Set default for DEVSTACK_GATE_USE_APACHE

If not set it throws an error(which is ignored) in devstack-vm-gate.sh.

Change-Id: Ib05a6e09714d386432ff31a4e40406ae7c1a55ca