fix executor names, clean up, remove code duplication

src/main/java/hudson/plugins/gearman/AbstractWorkerThread.java
    Removed Id field, it was initially added because I thought it was the plugin's
    responsibility to cancel jobs that are on the gearman queue.  We've decided that
    it will be the client (zuul or otherwise) responsibility to cancel jobs from the gearman
    queue.  The gearman plugin will cancel jobs that have already been put on the
    jenkins queue.

src/main/java/hudson/plugins/gearman/ComputerListenerImpl.java
src/main/java/hudson/plugins/gearman/ExecutorWorkerThread.java
src/main/java/hudson/plugins/gearman/GearmanPluginConfig.java
src/main/java/hudson/plugins/gearman/GearmanProxy.java
src/main/java/hudson/plugins/gearman/ManagementWorkerThread.java
src/main/java/hudson/plugins/gearman/StartJobWorker.java
    Refactor to reduce code duplication. Consolidated creation of management worker and
    executor workers.  Added a fix so that executors spawned on master node
    is named 'master-manager' for the manager and 'master-exec-#' for executors

src/test/java/hudson/plugins/gearman/ManagementWorkerThreadTest.java
    Added test to make sure worker name is set correctly

src/main/java/hudson/plugins/gearman/GearmanPluginUtil.java
src/test/java/hudson/plugins/gearman/GearmanPluginUtilTest.java
    Useful utils for the gearman plugin with tests

Change-Id: I96e097dc0dbf5cd78e5e82af584976085aee61b3
Merge "fix executor names, clean up, remove code duplication"