image-resin.bbclass: Define IMAGE_NAME_SUFFIX needed for older Yocto versions
image-resin.bbclass: Define IMAGE_NAME_SUFFIX needed for older Yocto versions

Yocto versions older than Morty, i.e. Jethro, do not define the IMAGE_NAME_SUFFIX variable
so we define it instead for these old versions.

Signed-off-by: Florin Sarbu <3a837a37a2ac9072a088641ec330e0e5d5b86f4e@resin.io>

resin-os/meta-resin,resin-os/meta-resin,resin-os/meta-resin,resin-os/meta-resin