Contribute if wall clock time is reached

[james-toussaint]

The worker should contribute if the wall clock time of the job is reached.
On container execution timeout, exit code is -1.
If we have such case, we should throw a WorkflowException and trigger post compute with something like CATEGORY_TIMEOUT_REACHED here:
https://github.com/iExecBlockchainComputing/iexec-worker/blob/develop/src/main/java/com/iexec/worker/executor/TaskManagerService.java#L234
In this case, an external developer will have a result archive.