Revert "Revert "Fixup app-private dirs that are not writable.""

Fixup non-writable app-private dirs that could have been left around by
an earlier race condition in the setup of the FUSE filesystem.

Bug: 181726193
Bug: 182088154
Test: erase userdata, check Youtube dirs are fixed up correctly

Reason for revert: fixing issue in original CL

Change-Id: Ifacf807f62dec3c9e22b5e5af0f2b00c4423ede4