Fix import statement order

Fix import statement order to comply with
OpenStack Style Guidelines(*1).

*1: http://docs.openstack.org/developer/hacking/#import-order-template

TrivialFix
Change-Id: I8ded09c14396a46f9d0f8f565d1294b179ce09bc

nova/tests/functional/db/test_aggregate.py

@@ -11,6 +11,7 @@
 #    under the License.
 
 from copy import deepcopy
+
 import mock
 from oslo_db import exception as db_exc
 from oslo_utils import timeutils
@@ -20,13 +21,12 @@ from nova import db
 from nova.db.sqlalchemy import api as db_api
 from nova.db.sqlalchemy import api_models
 from nova import exception
+import nova.objects.aggregate as aggregate_obj
 from nova import test
 from nova.tests.unit import matchers
 from nova.tests.unit.objects.test_objects import compare_obj as base_compare
 from nova.tests import uuidsentinel
 
-import nova.objects.aggregate as aggregate_obj
-
 
 SUBS = {'metadata': 'metadetails'}