Move test decorators to common

services and extension decorators are based on CONF and needed by
Tempest only, so moving them to tempest.common.
Since a few plugnis use them today, use debtcollector to avoid
breaking all dependencies.

Change-Id: Ibd52153d00b8e60fb8c89e38d94e358ddc787251
diff --git a/tempest/api/compute/servers/test_server_group.py b/tempest/api/compute/servers/test_server_group.py
index f402540..5286c8f 100644
--- a/tempest/api/compute/servers/test_server_group.py
+++ b/tempest/api/compute/servers/test_server_group.py
@@ -17,9 +17,9 @@
 
 from tempest.api.compute import base
 from tempest.common import compute
+from tempest.common import utils
 from tempest.lib.common.utils import data_utils
 from tempest.lib import decorators
-from tempest import test
 
 
 class ServerGroupTestJSON(base.BaseV2ComputeTest):
@@ -33,7 +33,7 @@
     @classmethod
     def skip_checks(cls):
         super(ServerGroupTestJSON, cls).skip_checks()
-        if not test.is_extension_enabled('os-server-groups', 'compute'):
+        if not utils.is_extension_enabled('os-server-groups', 'compute'):
             msg = "os-server-groups extension is not enabled."
             raise cls.skipException(msg)