Tez UI: Polling is not restarted after RM recovery

For a running DAG, we poll the AM to get progress and other realtime information. This communication happens via RM. If RM goes down, even after its recovery the polling is not re established.

Step to repro:
1. Run a job
2. Go to DAG details page, and ensure that the progress is getting updated.
3. Stop RM, and ensure that error bar is getting displayed in the UI.
4. Start RM.
5. As soon as RM is online, the progress bar must get updated.