Fixed: /var/lib/docker no longer shows up in DiskSpace. Caused warnings if the user used docker with zfs storage driver.

fixes #1663

src/NzbDrone.Mono/Disk/ProcMountProvider.cs

@@ -111,6 +111,12 @@ namespace NzbDrone.Mono.Disk
                 return null;
             }
 
+            if (mount.StartsWith("/var/lib/"))
+            {
+                // Could be /var/lib/docker when docker uses zfs. Very unlikely that a useful mount is located in /var/lib.
+                return null;
+            }
+
             var driveType = FindDriveType.Find(type);
 
             if (name.StartsWith("/dev/") || GetFileSystems().GetValueOrDefault(type, false))