Ensure Mockttp is properly shut down on clean exits

Author: pimterry

src/index.ts

@@ -24,7 +24,7 @@ import { IS_PROD_BUILD, MOCKTTP_ALLOWED_ORIGINS } from './constants';
 
 import { readFile, checkAccess, writeFile, ensureDirectoryExists } from './util/fs';
 
-import { registerShutdownHandler, shutdown } from './shutdown';
+import { addShutdownHandler, registerShutdownHandler, shutdown } from './shutdown';
 import { getTimeToCertExpiry, parseCert } from './certificates';
 
 import {
@@ -219,6 +219,8 @@ export async function runHTK(options: {
         host: '127.0.0.1'
     });
 
+    addShutdownHandler(() => standalone.stop());
+
     const standaloneSetupTime = Date.now();
     console.log('Standalone server started in', standaloneSetupTime - certSetupTime, 'ms');