Add load_balancer service if octavia is enabled

PROD-22019

Change-Id: I929e26259a384038a18af9d387c31ceb212396ab
diff --git a/_modules/runtest/tempest_sections/service_available.py b/_modules/runtest/tempest_sections/service_available.py
index a205f53..df288fd 100644
--- a/_modules/runtest/tempest_sections/service_available.py
+++ b/_modules/runtest/tempest_sections/service_available.py
@@ -23,6 +23,7 @@
         'swift',
         'horizon',
         'keystone',
+        'load_balancer',
     ]
 
     def _is_service_enabled(self, service):
@@ -119,3 +120,7 @@
     @property
     def keystone(self):
         return self._is_service_enabled('keystone')
+
+    @property
+    def load_balancer(self):
+        return self._is_service_enabled('octavia')