dnssec-policy inheritance from options/view

'dnssec-policy' can now also be set on the options and view level and
a zone that does not set 'dnssec-policy' explicitly will inherit it
from the view or options level.

This requires a new keyword to be introduced: 'none'.  If set to
'none' the zone will not be DNSSEC maintained, in other words it will
stay unsigned.  You can use this to break the inheritance.  Of course
you can also break the inheritance by referring to a different
policy.

The keywords 'default' and 'none' are not allowed when configuring
your own dnssec-policy statement.

Add appropriate tests for checking the configuration (checkconf)
and add tests to the kasp system test to verify the inheritance
works.

Edit the kasp system test such that it can deal with unsigned zones
and views (so setting a TSIG on the query).

bin/tests/system/kasp/ns5/template.db.in

@@ -0,0 +1,25 @@
+; Copyright (C) Internet Systems Consortium, Inc. ("ISC")
+;
+; This Source Code Form is subject to the terms of the Mozilla Public
+; License, v. 2.0. If a copy of the MPL was not distributed with this
+; file, You can obtain one at http://mozilla.org/MPL/2.0/.
+;
+; See the COPYRIGHT file distributed with this work for additional
+; information regarding copyright ownership.
+
+$TTL 300
+@		IN	SOA  mname1. . (
+			1       ; serial
+			20      ; refresh (20 seconds)
+			20      ; retry (20 seconds)
+			1814400 ; expire (3 weeks)
+			3600    ; minimum (1 hour)
+			)
+
+			NS	ns5
+ns5			A	10.53.0.5
+
+a			A	10.0.0.1
+b			A	10.0.0.2
+c			A	10.0.0.3
+