firewall: Add Host Firewall functionality

Controlled by BALENA_HOST_FIREWALL_MODE, the firewall can
either be 'on' or 'off'.

- In the 'off' state, all traffic is allowed.
- In the 'on' state, only traffic for the core services provided
  by Balena is allowed.

Change-type: patch
Signed-off-by: Rich Bayliss <rich@balena.io>

test/00-init.ts

@@ -6,6 +6,8 @@ process.env.DATABASE_PATH_2 = './test/data/database2.sqlite';
 process.env.DATABASE_PATH_3 = './test/data/database3.sqlite';
 process.env.LED_FILE = './test/data/led_file';
 
+import './lib/mocked-iptables';
+
 import * as dbus from 'dbus';
 import { DBusError, DBusInterface } from 'dbus';
 import { stub } from 'sinon';