Fix ocsp app exit code

If we run the ocsp command line app and the responder returns a
non-successful status code then the app should exit with a failure code.

Based on an original patch by Tatsuhiro Tsujikawa.

Fixes #2387

Reviewed-by: Rich Salz <rsalz@openssl.org>
Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/5999)