Merge "Add new handler mechanism in MountService to make unmount api...

Merge "Add new handler mechanism in MountService to make unmount api asynchronous. MountService updates state on PackageManager and then tries to kill processes holding file references to media about to be unmounted by invoking api on ACtivityManager. This is retried upto 4 times to make sure all processes holding file references are killed before unmounting the media at specified path."