The kasp system test requires Python

Only run the "kasp" system test if the path to the Python interpreter is
set.

bin/tests/system/kasp/prereq.sh

@@ -0,0 +1,19 @@
+#!/bin/sh
+#
+# 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 https://mozilla.org/MPL/2.0/.
+#
+# See the COPYRIGHT file distributed with this work for additional
+# information regarding copyright ownership.
+
+SYSTEMTESTTOP=..
+. $SYSTEMTESTTOP/conf.sh
+
+if ! test -n "$PYTHON"; then
+	echo_i "This test requires Python."
+	exit 1
+fi
+exit 0