Set promise result correctly when action is warn or in dry run.

The correct result when corrections should be made but are prevented
by warn-only is PROMISE_RESULT_WARN. Setting the result should be
done via PromiseResultUpdate to make sure that the various outcomes are
correctly combined.

Note: setting of promise result is missing in files_links.c:MakeLink,
verify_database.c:VerifyDatabasePromise. Several internal functions don't
allow propagating the promise result through the stack.