Add a claims listener that connects job claims to engines

To make it easily possible to stop running a engine that was
created from a job, add a claims listener that will be called
on state changes that an engine progresses through. During those
state changes the jobboard will be queried to determine if the
job is still claimed by the respective owner; if not the engine
will be suspended and further work will stop.

Change-Id: I8bbc6a3e03746ba0a7c74139cf9e230631d80d8f
Merge "Add a claims listener that connects job claims to engines"