Fix fetchlimit test failure

Fix fetchlimit test failure

When a referral lookup is triggered by a QMIN query, it should be
exempt from the fetches-per-zone limit just as the QMIN query itself
is.

Also restart the test server between the fetches-per-server and
fetches-per-zone tests so that leftover statistics from the former
do not pollute the latter.

Another fix is because zone spills and general query drops are no longer
in a strict >= relation (on a parent-centric resolver), so check that
both counters are non-zero instead.