Travis: The TLS 1.3 code isn't interoperable yet, move it to its own build

We should move it back to the BORINGTEST build when we are approaching
interoperability.

Reviewed-by: Kurt Roeckx <kurt@openssl.org>
Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/2123)