[test] Add self-tests for OCSP

Add self-tests for OCSP using test vectors generated with the openssl
tools.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/tests/tests.c

 REQUIRE_OBJECT ( bigint_test );
 REQUIRE_OBJECT ( rsa_test );
 REQUIRE_OBJECT ( x509_test );
+REQUIRE_OBJECT ( ocsp_test );
 REQUIRE_OBJECT ( cms_test );