Fix refreshing an already running app in iOS Simulator

Fix refreshing an already running app in iOS Simulator
Fixes http://teampulse.telerik.com/view#item/274387

 - kill all instances of running launcherd_sim to stop the running instances of the app.
 - use ios-sim with --exit parameter to ensure clean update

Return status 500 to clients when there's an error receiving the app package file