JpaJob object toString override for better log messages
Like but for JpaJob. Specifically to improve logging of:
2017-04-13 13:58:38,025 | DEBUG | pool-15-thread-1 | (ServiceRegistryJpaImpl$JobDispatcher:3037) - Unable to dispatch org.opencastproject.job.jpa.JpaJob@241a2c5b. This is likely caused by another service registry dispatching the job
2017-04-13 15:27:03,385 | DEBUG | pool-15-thread-2 | (ServiceRegistryJpaImpl$JobDispatcher:3113) - Unable to dispatch org.opencastproject.job.jpa.JpaJob@2a774b3c, no service is currently ready to accept the job
(and any similar log messages that include a JpaJob argument).