Reject accesses to app-private dirs on FUSE for emulated volumes.

Unfortunately, there's a small race condition where the FUSE filesystem
is mounted, but the bind-mounts of app-private data directories isn't
done yet. While apps technically shouldn't be accessing external storage
during this period (because we haven't signaled the volume is mounted
yet), apps that do end up creating app-private files with the wrong
permissions (of the MediaProvider process). To prevent this from
happening, reject these requests outright.

Bug: 181726193
Bug: 182088154
Test: atest
Change-Id: I3a766c9174e3378062a148433ffd4e9a26027da1
Merged-In: I3a766c9174e3378062a148433ffd4e9a26027da1
(cherry picked from commit ba3e67765949fb8352e3c5573b61f73e170d25bd)
1 file changed