CI: Don't create an external network in init-runonce

This network conflicts with the ironic provision-net since both are flat
networks on physnet1. We don't need the external network in our CI, so
don't create it.

Change-Id: Id17d4ea00ceb684b34bf12e911758d504c520de0
Depends-On: https://review.opendev.org/#/c/670129/

dev/functions

@@ -375,7 +375,11 @@ function overcloud_test_init {
     # This guards init-runonce from running more than once
     if mkdir /tmp/init-runonce > /dev/null 2>&1; then
         echo "Running kolla-ansible init-runonce"
+        # Don't create an external network, since it conflicts with the ironic
+        # provision-net.
+        export ENABLE_EXT_NET=0
         ${KOLLA_VENV_PATH:-$HOME/kolla-venv}/share/kolla-ansible/init-runonce
+        unset ENABLE_EXT_NET
     else
         echo "Not running kolla-ansible init-runonce - resources exist"
     fi