selftests: exit 1 on failure

In case this ever gets scripted, it should return 0 on success and 1 on
failure.  Parsing the output should be left to meatbags.

Signed-off-by: Joern Engel <joern@logfs.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>