[Fstab] Ignore docker overlay mounts

Docker overlay fs can be considered as a loop device and can be ignored.

BUG: 422385 FIXED-IN: 5.78 @broulik

Similar to 1384f275

An overlay fs appear currently in solid-hardware details as :

udi = '/org/kde/fstab/overlay/var/lib/docker/overlay2/3d557486b8f63fcdd70c697ef903bf849ccd9cc370f53df2deefad18b75e3dc2/merged'
  parent = '/org/kde/fstab'  (string)
  vendor = 'overlay'  (string)
  product = '/var/lib/docker/overlay2/3d557486b8f63fcdd70c697ef903bf849ccd9cc370f53df2deefad18b75e3dc2/merged'  (string)
  description = '/var/lib/docker/overlay2/3d557486b8f63fcdd70c697ef903bf849ccd9cc370f53df2deefad18b75e3dc2/merged (overlay)'  (string)
  icon = 'folder'  (string)
  StorageAccess.accessible = true  (bool)
  StorageAccess.filePath = '/var/lib/docker/overlay2/3d557486b8f63fcdd70c697ef903bf849ccd9cc370f53df2deefad18b75e3dc2/merged'  (string)
  StorageAccess.ignored = false  (bool)