Return a log level for a string

	>>> log_level('DEBUG') == logging.DEBUG
	True
	>>> log_level('30') == logging.WARNING
	True

def log_level(level_string):
	"""
	Return a log level for a string

	>>> log_level('DEBUG') == logging.DEBUG
	True
	>>> log_level('30') == logging.WARNING
	True
	"""
	if level_string.isdigit():
		return int(level_string)
	return getattr(logging, level_string.upper())