MXS-1739: Disable TLS session cache

Disabling the session cache prevents errors from being generated as the
default OpenSSL configuration is to enable session caching but with an
uninitialized context ID. In addition to preventing the errors, it
prevents the possible security problems implicated by the definition a
"static" context ID.

server/core/listener.c

@@ -290,6 +290,9 @@ listener_init_SSL(SSL_LISTENER *ssl_listener)
         /** Disable SSLv3 */
         SSL_CTX_set_options(ssl_listener->ctx, SSL_OP_NO_SSLv3);
 
+        // Disable session cache
+        SSL_CTX_set_session_cache_mode(ssl_listener->ctx, SSL_SESS_CACHE_OFF);
+
         /** Generate the 512-bit and 1024-bit RSA keys */
         if (rsa_512 == NULL && (rsa_512 = create_rsa(512)) == NULL)
         {