Fix import order to comply with import ordering rules.

Fixes pep8 failures TEMPEST N306 and N301.

Change-Id: I87d6ef4058170da73ff64d4e4a4caf43f8a18046
diff --git a/tempest/tests/compute/servers/test_disk_config.py b/tempest/tests/compute/servers/test_disk_config.py
index 1273fe4..638e093 100644
--- a/tempest/tests/compute/servers/test_disk_config.py
+++ b/tempest/tests/compute/servers/test_disk_config.py
@@ -19,10 +19,10 @@
 from nose.plugins.attrib import attr
 import unittest2 as unittest
 
-from tempest import exceptions
 from tempest.common.utils.data_utils import rand_name
-from tempest.tests.compute.base import BaseComputeTest
+from tempest import exceptions
 from tempest.tests import compute
+from tempest.tests.compute.base import BaseComputeTest
 
 
 class TestServerDiskConfig(BaseComputeTest):