add pre_test_hook file

we need this option for some tempest tests

Change-Id: I310c0c711aba8eb1aecea6c06c0998f35d5bfc62

devstack/pre_test_hook.sh

@@ -0,0 +1,18 @@
+#!/usr/bin/env bash
+# Copyright 2019 - Nokia
+#
+# Licensed under the Apache License, Version 2.0 (the "License"); you may
+# not use this file except in compliance with the License. You may obtain
+# a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+# License for the specific language governing permissions and limitations
+# under the License.
+
+DEVSTACK_PATH="$BASE/new"
+
+