Make sqlite in-memory-db usable to unittest

Move migrate monkey patch from nova.tests.test_migrations to
nova.db.sqlalchemy.migration

Change-Id: I018e44903558cad6311fd368787583322f962d0c

nova/test.py

@@ -40,6 +40,7 @@ from nova.openstack.common import cfg
 from nova import utils
 from nova import service
 from nova.testing.fake import rabbit
+from nova.tests import reset_db
 from nova.virt import fake
 
 
@@ -129,8 +130,7 @@ class TestCase(unittest.TestCase):
         #             now that we have some required db setup for the system
         #             to work properly.
         self.start = utils.utcnow()
-        shutil.copyfile(os.path.join(FLAGS.state_path, FLAGS.sqlite_clean_db),
-                        os.path.join(FLAGS.state_path, FLAGS.sqlite_db))
+        reset_db()
 
         # emulate some of the mox stuff, we can't use the metaclass
         # because it screws with our generators