In case of an invalid DH parameter file, it is sliently discarded. To
use auto DH parameter in a server and DHE key length check in a
client, we need to wait for the next release of OpenSSL-1.0.2.
Reviewed-By: Fedor Indutny <fedor@indutny.com>
Move `createCredentials` to `tls` module and rename it to
`createSecureContext`. Make it use default values from `tls` module:
`DEFAULT_CIPHERS` and `DEFAULT_ECDH_CURVE`.
fix#7249