When merging develop into disposable-develop, I missed some changes in runner.py related to exitcode directive implementation (D447) and broke the runner. I tried to fix that in rLTRNfcd7200ad3a, but I made a logical mistake there (task_runner is never LocalRunner instance there, always Runner instance) and therefore effectively disable the whole exitcode_directive.

We need to fix that, and we should also think about propagating that exit code through RemoteRunner, so that the directive works properly even when run remotely (e.g. on a disposable client).

@lbrabec, can you please look at it? Thanks.