Upgrade isotesters to Linux 4.9.0-3

i.e. revert commits c1d03c16d057875302f6ef86bd73145b36a6d5dd and 946ea373fe55f69fce3f6c804874c66c100d574f in our manifests repo once https://bugs.debian.org/865343 is fixed in Stretch.

Related issues

Related to #13138 (closed)

Original created by @intrigeri on 13180 (Redmine)

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