Simplify xml-json inheritance in compute

_interface just specified in the real test classes.

Change-Id: I40fc6fe4d1a00fa0d83c4343feba73e3192f0991
diff --git a/tempest/tests/compute/test_authorization.py b/tempest/tests/compute/test_authorization.py
index d826d40..52e457d 100644
--- a/tempest/tests/compute/test_authorization.py
+++ b/tempest/tests/compute/test_authorization.py
@@ -22,10 +22,11 @@
 from tempest.common.utils.data_utils import rand_name
 from tempest import exceptions
 from tempest.tests import compute
-from tempest.tests.compute.base import BaseComputeTest
+from tempest.tests.compute import base
 
 
-class AuthorizationTest(BaseComputeTest):
+class AuthorizationTest(base.BaseComputeTest):
+    _interface = 'json'
 
     @classmethod
     def setUpClass(cls):
@@ -243,6 +244,7 @@
             # Reset the base_url...
             self.alt_security_client.base_url = self.saved_base_url
             if resp['status'] is not None:
+                #TODO(afazekas): body not defined
                 self.alt_security_client.delete_security_group(body['id'])
                 self.fail("Create Security Group request should not happen if"
                           "the tenant id does not match the current user")
@@ -283,7 +285,7 @@
             self.alt_security_client.base_url = self.saved_base_url
             if resp['status'] is not None:
                 self.alt_security_client.delete_security_group_rule(
-                                        body['id'])
+                                        body['id'])  # BUG
                 self.fail("Create security group rule request should not "
                           "happen if the tenant id does not match the"
                           " current user")