As part of contrail-vrouter-agent NodeStatus UVE, send the status as NON-FUNCTIONAL only when all the agent's connection to control-node is down. In all other cases, agent reports the state as FUNCTIONAL.
Add UT cases.
Closes-Bug: #1396164

Change-Id: I3336bfb9eae9810307619ccb08e52a76322a24bf
(cherry picked from commit 90021d5f8e212c0de6e82084f93a50691f347b5f)