Fix SquashFS sort file update slows down boot

Since May 2013, when we tried updating config/binary_rootfs/squashfs.sort, it actually made things worse.

Feature Branch: bugfix/6372-squashfs-sort-file-update

Original created by @intrigeri on 6372 (Redmine)

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information