If cells enabled create a fixed network in the API cell

Now that tempest is querying for a network before making server create
calls the fixed network needs to be known by the API cell.  Server
creates should work for networks defined in both databases, but defining
a new network via the API will continue to not work.

Change-Id: I32461add0d20940a55385c8b34cd493e2561615e
diff --git a/stack.sh b/stack.sh
index 8ab8234..adcaa21 100755
--- a/stack.sh
+++ b/stack.sh
@@ -1214,6 +1214,9 @@
 elif is_service_enabled $DATABASE_BACKENDS && is_service_enabled n-net; then
     NM_CONF=${NOVA_CONF}
     if is_service_enabled n-cell; then
+        # Create a small network in the API cell
+        $NOVA_BIN_DIR/nova-manage --config-file $NM_CONF network create "$PRIVATE_NETWORK_NAME" $FIXED_RANGE 1 $FIXED_NETWORK_SIZE $NETWORK_CREATE_ARGS
+        # Everything else should go in the child cell
         NM_CONF=${NOVA_CELLS_CONF}
     fi