Add SSL_CONF support to ssltest.

Add command line support for SSL_CONF: server side arguments are
prefixed by -s_ (e.g. -s_no_ssl3) and client side with -c_.
Reviewed-by: Matt Caswell <matt@openssl.org>
Additional output for ssltest.

Print out more details of the conection in ssltest specifically:
server certificate curve name for EC, server temporary key (if any)
and peer signing digest.
Reviewed-by: Matt Caswell <matt@openssl.org>