Use service tagging 'decorators'

The test 'test_extend_attached_volume' makes api call to
nova which is differ from the parent directory name(volume).

Change-Id: I68962bf7a04fcb73412c94700c8301d170b3b1a3
diff --git a/tempest/api/volume/test_volumes_extend.py b/tempest/api/volume/test_volumes_extend.py
index de28a30..b73bdf2 100644
--- a/tempest/api/volume/test_volumes_extend.py
+++ b/tempest/api/volume/test_volumes_extend.py
@@ -18,6 +18,7 @@
 import testtools
 
 from tempest.api.volume import base
+from tempest.common import utils
 from tempest.common import waiters
 from tempest import config
 from tempest.lib import decorators
@@ -104,6 +105,7 @@
     @decorators.idempotent_id('301f5a30-1c6f-4ea0-be1a-91fd28d44354')
     @testtools.skipUnless(CONF.volume_feature_enabled.extend_attached_volume,
                           "Attached volume extend is disabled.")
+    @utils.services('compute')
     def test_extend_attached_volume(self):
         """This is a happy path test which does the following: