Add TLS 1.3 certificate selection tests.

For TLS 1.3 we select certificates with signature algorithms extension
only. For ECDSA+SHA384 there is the additional restriction that the
curve must be P-384: since the test uses P-256 this should fail.

Reviewed-by: Rich Salz <rsalz@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/2339)