Simplify / document process of adding new tests for TLS

[dadrian]

We use the tests for TLS from Golang in 2014. We should probably be pulling in the TLS tests from Golang 1.8. Additionally, we don't have good tests for our new ciphers that aren't in Golang stdlib (e.g. export ciphers).

The test runner compares a "deterministic" TLS handshake to a hex dump of a handshake with OpenSSL. We should figure out how this works, document/script it, and make it easier to add new tests of this form for when we add features.