Trivial: group import statement in client.py

Add extra lines to fit the hacking rule in [1].

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

Change-Id: I3330a8649532164670d10ad2eebf49e62635f042
diff --git a/tempest/clients.py b/tempest/clients.py
index 4c677f0..b13b809 100644
--- a/tempest/clients.py
+++ b/tempest/clients.py
@@ -14,7 +14,9 @@
 #    under the License.
 
 import copy
+
 from oslo_log import log as logging
+
 from tempest.common import negative_rest_client
 from tempest import config
 from tempest import exceptions