image_types.bbclass: tar: Override change in tar --format back to 'gnu'
A patch in poky/meta-openembedded-code changed the format to posix: https://github.com/openembedded/openembedded-core/commit/3ecea58f2a3382d9f4b410d6ad7089111334cb6f.
This overrides the change in the DISTRO include variable to previous value of IMAGE_CMD_tar, as the posix format is not compatible to the old tar versions from FNGSystem Version < 16, resulting in heaps of warnings.
Edited by Tobias Kahlki