Unmount device (or mount directory)

		:param device_or_directory: device name or mount directory to unmount
		:param cmd_timeout: if specified - timeout with which this unmount command should be evaluated (if \
		command isn't complete within the given timeout - an exception will be raised)
		:param sudo: whether to use sudo to run mount command

		:return: None

def umount(cls, device_or_directory, cmd_timeout=None, sudo=False):
		""" Unmount device (or mount directory)

		:param device_or_directory: device name or mount directory to unmount
		:param cmd_timeout: if specified - timeout with which this unmount command should be evaluated (if \
		command isn't complete within the given timeout - an exception will be raised)
		:param sudo: whether to use sudo to run mount command

		:return: None
		"""
		cmd = [] if sudo is False else ['sudo']
		cmd.extend(['umount', device_or_directory])
		subprocess.check_output(cmd, timeout=cmd_timeout)