Fails if there are spaces in one USB-Stick's label

[lalten]

It may not be smart to have spaces in paths (e.g. /media/laurenz/Timeshift Backup), but from time to time it will still happen.

[ERROR] [1530271672.198548]: Traceback (most recent call last):                                                                                                                                                     
  File "/home/laurenz/catkin_ws/src/ros-system-monitor/bin/hdd_monitor.py", line 275, in check_disk_usage                                                                                                           
    hdd_usage = float(g_use.replace("%", ""))*1e-2                                                                                                                                                                  
ValueError: could not convert string to float: /media/laurenz/Timeshift