deadlocks and similar.

…eled

jobs and spam the pytest suite, since pytest doesn't capture the log after
the test is done.

special devices which bash will happily emulate if not found.

Since the addition of staging, errors can reasonably occur outside of
the launcher as well as inside the launcher and pre- and post- launch
scripts. So we treat the output of the whole script (including launcher)
as potential indicator of an error.

…s to

CWD (the CI runner runs things in /tmp).

…to avoid

clashes with other things that might be defined in the environment.
- use `StageOutFlags` to express when cleanup happens rather than a boolean
flag
- fixed equality operator in `JobSpec`
- added `__str__`, `__eq__` and `__hash__` methods for staging objects