Added unit tests to protect against broken startup sequence

Summary: Add unit tests to test errors thrown from plugins during initialisation, as follow up for D31127969 (a72e46c792). From the 4 tests cases added (first load plugin then device, device then plugin, first load plugin then client, first client then plugin), the first case was indeed failing before the mentioned diff and not registering the device.

Reviewed By: passy

Differential Revision: D31142583

fbshipit-source-id: 8e44c667316192231d1bb5e4d76c5bf1207ba835

desktop/flipper-plugin/src/__tests__/api.node.tsx

@@ -102,6 +102,7 @@ test('Correct top level API exposed', () => {
       "LogTypes",
       "Logger",
       "MenuEntry",
+      "MockedConsole",
       "NormalizedMenuEntry",
       "Notification",
       "PluginClient",