Duplicate logging output during MPI testing.

[oskar-taubert]

During testing output from the logger is printed multiple times.
The number of prints depends on the number of tests already run.
This is fixed in the sequential tests in #maintenance/checkpointing.
The logger is probably created multiple times somewhere.
If possible we should catch and fix this centrally.

[oskar-taubert]

Solution is to call
set_logger_config()
at the beginning of each test and
log.handlers.clear()
at the end of each test.
log is
log = logging.getLogger("propulate")
at the beginning of the test module.