This command will be used in tests so tests won't mount data and obb
dirs anymore so won't be killed by system when volume is unmounted.
Bug: 148049767
Test: Enable storage app visibility flag, then run "sm unmount-app-data-dirs PKG PID USER_ID", data and obb are not mounted in /proc/$PID anymore.
Change-Id: Ie5ddf55471f59c61e1906664b87a9bf889702536