crypto: support multiple ECDH curves and auto

Using SSL_CTX_set1_curves_list() (OpenSSL 1.0.2+), this allows to set
colon separated ECDH curve names in SecureContext's ecdhCurve option.
The option can also be set to "auto" to select the curve automatically
from list built in OpenSSL by enabling SSL_CTX_set_ecdh_auto()
(OpenSSL 1.0.2+).

PR-URL: https://github.com/nodejs/node/pull/15206
Ref: https://github.com/nodejs/node/issues/15054


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>