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.