New sm command to unmount app data and obb app visibility mount

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