Move data-driven-upgrade test imports from run_tests.py

Old-way test import produces merge conflict each time when new test
is added for suite and cherry-picked from mitaka to 8.0 branch.
Moving imports out of run_tests.py removes this behaviour.

Test discovering mechanism used in mitaka and master branch ignores
imports in __init__ file.

Change-Id: Ic822afc1f4ef8d65800fed379b0840320566c398

fuelweb_test/tests/tests_upgrade/__init__.py

@@ -0,0 +1,16 @@
+#    Copyright 2016 Mirantis, Inc.
+#
+#    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.
+
+from fuelweb_test.tests.tests_upgrade import test_data_driven_upgrade  # noqa
+from fuelweb_test.tests.tests_upgrade import upgrader_tool  # noqa