Test suite: disable OCSP for old OpenSSL versions

OpenSSL 0.9.8 in CentOS 5.x has early OCSP support, but not stapling
  so just completely disable OCSP using the same logic that exists
  in tls-openssl.c.
Test suite: disable OCSP for old openssl part 2

Make sure to only disable this if building for openssl, allow gnutls
  to build with OCSP for all versions that support it.