Assign default value of ltm resources

(cherry picked from commit f06e9d9)

Author: zhaoqin-github

f5lbaasdriver/v2/bigip/service_builder.py

@@ -152,6 +152,14 @@ def build(self, context, loadbalancer, agent, **kwargs):
                         net_type
                     )
 
+            # Assign default values
+            service['listeners'] = []
+            service['pools'] = []
+            service['healthmonitors'] = []
+            service['members'] = []
+            service['l7policies'] = []
+            service['l7policy_rules'] = []
+
             # Get listeners and pools.
             append_listeners = kwargs.get(
                 "append_listeners", self._append_listeners)