Exceptions raised with pytest 5.0

[rouault]

pytest 5.0 no longer supports python 2.7, fair enough
more annoying, with python 3, our autotest suite doesn't pass with pytest 5 due to use of deprecated features, such as the 'message' argument of pytest.raises()

>       with pytest.raises(OSError, message='small.rrd still present.'):
E       pytest.PytestDeprecationWarning: The 'message' parameter is deprecated.
E       (did you mean to use `match='some regex'` to check the exception message?)
E       Please see:
E         https://docs.pytest.org/en/4.6-maintenance/deprecations.html#message-parameter-of-pytest-raises

hfa_write.py:164: PytestDeprecationWarning

See https://docs.pytest.org/en/latest/deprecations.html#message-parameter-of-pytest-raises