Make logging configurable

[gerritholl]

Logging configuration is currently hardcoded in viirs_dr_runner.py:

pytroll-cspp-runner/bin/viirs_dr_runner.py

Lines 730 to 736 in 780e481

	handler.setLevel(logging.DEBUG)
	formatter = logging.Formatter(fmt=_DEFAULT_LOG_FORMAT,
	datefmt=_DEFAULT_TIME_FORMAT)
	handler.setFormatter(formatter)
	logging.getLogger('').addHandler(handler)
	logging.getLogger('').setLevel(logging.DEBUG)
	logging.getLogger('posttroll').setLevel(logging.INFO)

It would be more user-friendly if this could be configured with a logging config, such as used by trollflow2.