Check that pending negative cache entries for DS can be used successfully
requested to merge 3279-lib-dns-ncache-c-rdataset_settrust-fails-to-set-trust-on-called-rdataset-v9_18 into v9_18
Prime the cache with a negative cache DS entry then make a query for name beneath that entry. This will cause the DS entry to be retieved as part of the validation process. Each RRset in the ncache entry will be validated and the trust level for each will be updated.
(cherry picked from commit d2d9910d)
Closes #3279 (closed)