Better error handling in the example script
Better error handling in the example script

Exit with non-zero status if any error occurs when setting up
the Gerrit connection or when starting the event stream.

Also make sure the event stream is stopped before exiting.

Change-Id: Ibf3742b834e30a019fa952440277f9027b8e85ea

markon/pygerrit2,dpursehouse/pygerrit2,gferon/pygerrit2,morucci/pygerrit,sonyxperiadev/pygerrit,dpursehouse/pygerrit,benjiii/pygerrit