waf: improve readability of cross-answers generated by cross-execute

waf: improve readability of cross-answers generated by cross-execute

When generating a result for cross-answers from the (retcode, retstring) tuple:
- (0, "output") indicated as "output"
- 1 is interpreted as generic fail code, instead of 255, because most
  if not all tests fail with 1 as exit code rather than 255
- For failing test, use NO instead of FAIL, because that's not
  necessarily a failure (it could mean that something is NOT
  broken)

Signed-off-by: Uri Simchoni <urisimchoni@gmail.com>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>
Reviewed-by: Alexander Bokovoy <ab@samba.org>