Update to enable gearman to Grab UUID from client

This fix is driven by a bug fix in gearman-java.  The bug fix enabled
Gearman worker to get the job id from the client
(https://bugs.launchpad.net/gearman-java/+bug/1098816)

src/main/java/hudson/plugins/gearman/AbstractWorkerThread.java
    set the worker to perform GRAB_JOB_UNIQ

src/main/java/hudson/plugins/gearman/StartJobWorker.java
    Get and decode the job UUID from gearman client

src/main/java/hudson/plugins/gearman/StopJobWorker.java
    Get and decode the job UUID from gearman client
    Remove cancelBuild method because it's not needed when using the gearman plugin,
    the gearman queue replaces the jenkins queue.
    Put in a stub for cancelJob method to cancel jobs from the Gearman queue.

src/main/java/hudson/plugins/gearman/example/StopJobClient.py
    minor update - don't need to send in data for stop job.

Change-Id: Ie3bb512cf17796091970fec4fa4c7afd05592bdb