Add inline-signing with $INCLUDE test

Add a test case for inline-signing for a zone with an $INCLUDE
statement. There is already a test for a missing include file, this
one adds a test for a zone with an include file that does exist.

Test if the record in the included file is loaded.

(cherry picked from commit 6463ee0f40)

bin/tests/system/inline/ns3/master7.db.in

@@ -0,0 +1,24 @@
+; 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.
+
+$TTL 300	; 5 minutes
+@			IN SOA	ns3 . (
+				2000042412 ; serial
+				20         ; refresh (20 seconds)
+				20         ; retry (20 seconds)
+				1814400    ; expire (3 weeks)
+				3600       ; minimum (1 hour)
+				)
+			NS	ns3
+ns3			A	10.53.0.3
+
+c			A	10.0.0.3
+e			A	10.0.0.5
+
+$INCLUDE include.db