Ensure example abandons job when it fails

If a worker can't finish a job and the worker has not
crashed it should make sure that it manually abandons
the job that it claimed (if it crashes this release will
happen automatically).

Change-Id: I2d6894281915fd335bffa34c006aed023e88e9fc

doc/source/jobs.rst

@@ -145,6 +145,7 @@ might look like:
                 perform_job(my_job)
             except Exception:
                 LOG.exception("I failed performing job: %s", my_job)
+                board.abandon(my_job, my_name)
             else:
                 # I finished it, now cleanup.
                 board.consume(my_job)