Test that we reject RSA ServerKeyExchange more thoroughly.

The old test just sent an empty ServerKeyExchange which is sufficient as we
reject the message early. But be more thorough and implement the actual
ephemeral key logic in the test server.

Change-Id: I016658762e4502c928c051e14d69eea67b5a495f
Reviewed-on: https://boringssl-review.googlesource.com/3650
Reviewed-by: Adam Langley <agl@google.com>
4 files changed