Change to test JSON msgs are case-insensitive.

Fix hard coded use of load balancer list name field. Also make
sure our tests use a mixed case version of this field name to
verify we still recognize it properly.

Change-Id: I48954f619dab8df85339b65495b342a52edfead1

libra/worker/controller.py

@@ -105,7 +105,7 @@ class LBaaSController(object):
                 "Missing '%s' element" % self.LBLIST_FIELD
             ).to_json()
 
-        lb_list = self.msg['loadbalancers']
+        lb_list = self.msg[self.LBLIST_FIELD]
 
         for current_lb in lb_list:
             if 'nodes' not in current_lb: