Support: serverCloseComplete option (#5937)

* Support: serverCloseComplete option

Callback when server has fully shutdown.

Please check that all cases are covered.

* handle error on startup

* fix tests

* test workaround

* remove serverCloseComplete chech on startup failure

src/Options/index.js

@@ -199,8 +199,10 @@ export interface ParseServerOptions {
   :ENV: PARSE_SERVER_PLAYGROUND_PATH
   :DEFAULT: /playground */
   playgroundPath: ?string;
-
+  /* Callback when server has started */
   serverStartComplete: ?(error: ?Error) => void;
+  /* Callback when server has closed */
+  serverCloseComplete: ?() => void;
 }
 
 export interface CustomPagesOptions {