Check for glance service for glance tests

test_unified_limits scenario test the image service
limits and we should check the glance service is enable
or not. Adding it in skip_checks method which run very
first thing (before resource_setup()) to start the test.

Change-Id: I86637ae2fd4e00ce5571d7fac8ae41418637cf29
diff --git a/tempest/scenario/test_unified_limits.py b/tempest/scenario/test_unified_limits.py
index 6e194f9..7e8f8b2 100644
--- a/tempest/scenario/test_unified_limits.py
+++ b/tempest/scenario/test_unified_limits.py
@@ -32,6 +32,13 @@
     credentials = ['primary', 'system_admin']
 
     @classmethod
+    def skip_checks(cls):
+        super(ImageQuotaTest, cls).skip_checks()
+        if not CONF.service_available.glance:
+            skip_msg = ("%s skipped as glance is not available" % cls.__name__)
+            raise cls.skipException(skip_msg)
+
+    @classmethod
     def resource_setup(cls):
         super(ImageQuotaTest, cls).resource_setup()