Add migration.py based on the one in nova.

This adds a migration.py file for setup and migration commands
similar to the file in nova. This was needed for porting the
new test migration framework.

Change-Id: Ic4d3a5e471b5fb8ee38b22b97df2e99b9fb649a1

glance/db/migration.py

@@ -0,0 +1,40 @@
+# vim: tabstop=4 shiftwidth=4 softtabstop=4
+
+# Copyright 2010 United States Government as represented by the
+# Administrator of the National Aeronautics and Space Administration.
+# All Rights Reserved.
+#
+# Copyright 2013 OpenStack Foundation
+# Copyright 2013 IBM Corp.
+#
+#    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.
+
+"""Database setup and migration commands."""
+
+from glance.common import utils
+
+
+IMPL = utils.LazyPluggable('db_backend',
+                           sqlalchemy='glance.db.sqlalchemy.migration')
+
+INIT_VERSION = 000
+
+
+def db_sync(version=None):
+    """Migrate the database to `version` or the most recent version."""
+    return IMPL.db_sync(version=version)
+
+
+def db_version():
+    """Display the current database version."""
+    return IMPL.db_version()