Add test for CT_POLICY_EVAL_CTX default time

Checks that the epoch_time_in_ms field of CT_POLICY_EVAL_CTX is initialized
to approximately the current time (as returned by time()) by default. This
prevents the addition of this field, and its verification during SCT
validation, from breaking existing code that calls SCT_validate directly.

Reviewed-by: Viktor Dukhovni <viktor@openssl.org>
Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/1554)