des_read_pw_string not supported by BoringSSL
des_read_pw_string not supported by BoringSSL

Motivation:
des_read_pw_string is not supported by BoringSSL and explicitly used by an ifdef is BoringSSL is being used.

Modifications:
- The SSL_password_prompt should not call des_read_pw_string when BoringSSL is used, and should return failure

Result:
des_read_pw_string is not used for BoringSSL.
Fixes https://github.com/netty/netty-tcnative/issues/63

floragunncom/netty-tcnative,netty/netty-tcnative,netty/netty-tcnative,netty/netty-tcnative,floragunncom/netty-tcnative,netty/netty-tcnative