Add a test for RSA key exchange with both RSA and RSA-PSS certs

Check that we use an RSA certificate if an RSA key exchange ciphersuite
is being used and we have both RSA and RSA-PSS certificates configured.

Reviewed-by: Paul Dale <paul.dale@oracle.com>
Reviewed-by: Tim Hudson <tjh@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7099)