Adapt host configuration

Adapt the configuration of the test hosts to the new Debian-based
system.

testing/hosts/default/etc/iptables.flush

@@ -0,0 +1,21 @@
+*filter
+
+-F
+
+-P INPUT ACCEPT
+-P OUTPUT ACCEPT
+-P FORWARD ACCEPT
+
+COMMIT
+
+*nat
+
+-F
+
+COMMIT
+
+*mangle
+
+-F
+
+COMMIT