Use shared signature algorithm list to find type.

Lookup the signature type in the shared list: we can use this to
use PSS if the peer supports it for TLS 1.2.

Reviewed-by: Richard Levitte <levitte@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/2301)