Add list-devices option to list the available devices.

Summary: This diff adds an option of `--list-devices` which will list the currently active devices on the machine. It will be later used to select a device by passing an `id` as an argument.

Reviewed By: danielbuechele

Differential Revision: D15524250

fbshipit-source-id: 7a79ceb1e431a25adcb4e05bc0cb68407c527806

src/utils/listDevices.js

@@ -0,0 +1,15 @@
+/**
+ * Copyright 2018-present Facebook.
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ * @format
+ */
+import {getActiveAndroidDevices} from '../dispatcher/androidDevice';
+import {getActiveDevicesAndSimulators} from '../dispatcher/iOSDevice';
+import type BaseDevice from '../devices/BaseDevice';
+
+export async function listDevices(): Promise<Array<BaseDevice>> {
+  const androidDevices = await getActiveAndroidDevices();
+  const iOSDevices = await getActiveDevicesAndSimulators();
+  return iOSDevices.concat(androidDevices);
+}