Do not block for device manager to become ready

Summary:
^

Also, if an error happens, do not swallow it, rethrow.

Reviewed By: passy

Differential Revision: D49912780

fbshipit-source-id: 30451110d8c5776e2b0826d6e924ab5fe98cd7e2

desktop/flipper-server-core/src/FlipperServerImpl.tsx

@@ -199,13 +199,17 @@ export class FlipperServerImpl implements FlipperServer {
       await this.createFolders();
       await this.server.init();
       await this.pluginManager.start();
-      await this.startDeviceListeners();
+
+      this.startDeviceListeners();
+
       this.setServerState('started');
     } catch (e) {
       if (!isHandledStartupError(e)) {
         console.error('Failed to start FlipperServer', e);
       }
       this.setServerState('error', e);
+
+      throw e;
     }
   }