Simplify job poll

The status of job is:
* submitted: job in queueing system, has no status file.
* submission failed: job not in queueing system, has no status file.
* running: job in queueing system, has status file.
* succeeded/failed: job not in queueing system, has status file.
cylc get-job-status tests
test: use >&2 instead of >/dev/tty

There may not be one.