Revert "Update a test to work with Quantum SecGroup"

This reverts commit 2c2978703319631f1c0144db05f55dbad3a55c50

The correct patch has been submitted by Melanie Witt here :
https://review.openstack.org/#/c/30815/
diff --git a/tempest/api/compute/servers/test_servers_negative.py b/tempest/api/compute/servers/test_servers_negative.py
index 25a7522..b369179 100644
--- a/tempest/api/compute/servers/test_servers_negative.py
+++ b/tempest/api/compute/servers/test_servers_negative.py
@@ -236,11 +236,7 @@
         # Create a server with a nonexistent security group
 
         security_groups = [{'name': 'does_not_exist'}]
-        if self.config.network.quantum_available:
-            expected_exception = exceptions.NotFound
-        else:
-            expected_exception = exceptions.BadRequest
-        self.assertRaises(expected_exception,
+        self.assertRaises(exceptions.BadRequest,
                           self.create_server,
                           security_groups=security_groups)