Bind to localhost in newly generated configs

This improves security by preventing connections from other computers. The
old behavior of binding to all network interfaces can still be enabled by
removing the listenAddress field from the config or setting it to "*".

lib/examples/default_config.mjs

@@ -15,6 +15,15 @@ export default {
     stopOnSpecFailure: false,
     random: true
   },
+
+  // For security, listen only to localhost. You can also specify a different
+  // hostname or IP address, or remove the property or set it to "*" to listen
+  // to all network interfaces.
+  listenAddress: "localhost",
+
+  // The hostname that the browser will use to connect to the server.
+  hostname: "localhost",
+
   browser: {
     name: "firefox"
   }

lib/examples/default_esm_config.mjs

@@ -19,6 +19,15 @@ export default {
     stopOnSpecFailure: false,
     random: true
   },
+
+  // For security, listen only to localhost. You can also specify a different
+  // hostname or IP address, or remove the property or set it to "*" to listen
+  // to all network interfaces.
+  listenAddress: "localhost",
+
+  // The hostname that the browser will use to connect to the server.
+  hostname: "localhost",
+
   browser: {
     name: "firefox"
   }