Run on-demand self-tests when requested

Run on-demand self-tests when requested

The `on_demand_test` flag passed to `SELF_TEST_post` was not being honored by
the Known Answer Test (KAT) runner. Tests marked as 'deferred' were always
skipped.

This change passes the `on_demand_test` flag through to the KAT functions,
ensuring that when an on-demand test is requested, the full suite of self-
tests is executed as intended.

Signed-off-by: Simo Sorce <simo@redhat.com>
Reviewed-by: Paul Dale <paul.dale@oracle.com>
Reviewed-by: Shane Lontis <shane.lontis@oracle.com>
Reviewed-by: Dmitry Belyavskiy <beldmit@gmail.com>
(Merged from https://github.com/openssl/openssl/pull/28725)