Actually finish the promise when submitting jobs

Change-Id: I1a788c2173a3700ccd4f07b955c92d6f1733d013
Maximum execution times for backend processes

Using the max_execution_time parameter in the config file, the backend
thread will enforce maximum execution times for backend tasks. When
the task is to be killed it will be sent a SIGTERM.

Change-Id: I75ba51d81364eab439239d00b975908bc633301f