Avoid having log messages stuck in a pipe when stdout is not a tty,
e.g. when running a suite of tests using 9pm.
Two benefits:
- Nicer experience when interactively running a suite
- Timestamps inserted by 9pm are more useful
It is not uncommon for subprocesses to fail when developing new tests,
but the default representation of CalledProcessError does not print
the stdout of the program, only that it failed.
Catch this common case when a test is about to fail, and make sure to
log any output it produced.
Tobias Waldekranz