Check that minimal NSEC records are not cached

construct a test zone which contains a minimal NSEC record,
emit priming queries for this record, and then check that
a respose that would be synthesised from it isn't.

bin/tests/system/synthfromdnssec/ns1/root.db.in

@@ -15,3 +15,5 @@ example		NS	ns1.example
 ns1.example	A	10.53.0.1
 dnamed		NS	ns1.dnamed
 ns1.dnamed	A	10.53.0.1
+minimal		NS	ns1.minimal
+ns1.minimal	A	10.53.0.1