backward_incompat: Don't use SHA1 files

backward_incompat: Don't use SHA1 files

SHA1 files can be changed between versions, due to that, we won't skip
those type and still fail to test them.
use empty directory with the type name to skip all files for
backward_incompat instead.

Signed-off-by: Nitzan Mordechai <nmordech@ibm.com>