Add server group limits in test_absLimits_get

Limits about server groups are missing in test_absLimits_get,
see
http://developer.openstack.org/api-ref/compute/?expanded=
show-rate-and-absolute-limits-detail#show-rate-and-absolute-limits

This is to add missing limit items about server group.

Change-Id: If7f62293daa82cdca848d141216dd75386d452ed
diff --git a/tempest/api/compute/limits/test_absolute_limits.py b/tempest/api/compute/limits/test_absolute_limits.py
index 69811f4..6cc722c 100644
--- a/tempest/api/compute/limits/test_absolute_limits.py
+++ b/tempest/api/compute/limits/test_absolute_limits.py
@@ -35,9 +35,10 @@
                              'maxTotalFloatingIps', 'maxSecurityGroups',
                              'maxSecurityGroupRules', 'maxTotalInstances',
                              'maxTotalKeypairs', 'maxTotalRAMSize',
+                             'maxServerGroups', 'maxServerGroupMembers',
                              'totalCoresUsed', 'totalFloatingIpsUsed',
                              'totalSecurityGroupsUsed', 'totalInstancesUsed',
-                             'totalRAMUsed']
+                             'totalRAMUsed', 'totalServerGroupsUsed']
         # check whether all expected elements exist
         missing_elements =\
             [ele for ele in expected_elements if ele not in absolute_limits]