crypto: use SSL_get_servername.

(Patch by David Benjamin.)

Rather than reach into the SSL_SESSION, use the intended API,
SSL_get_servername. This will also help the transition to OpenSSL 1.1.0.

Also don't fill in the tlsTicket field here. This is never read by
oncertcb and was always false anyway; that field is maintained by
clients and tracks whether the server issued a ticket or a session ID.

(Note this is distinct from the copy passed to onclienthello which is
used and is not a no-op.)

PR-URL: https://github.com/nodejs/node/pull/9347


Reviewed-By: Fedor Indutny <fedor@indutny.com>
Reviewed-By: Shigeki Ohtsu <ohtsu@ohtsu.org>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>