Restrict access to directories

Restricted access to Android/data, Android/obb and Android/sandbox
directories and its sub-directories. Replacing path's pattern match
check with file equality check.

Test: atest DocumentsClientTest
Bug: 341680936
Flag: EXEMPT bug fix
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:3ebd6405d2e87e6df0887d76470e4b7504bd3a4d)
Merged-In: I8879900e57e1702d11797b81e86d0cc3f55bac22
Change-Id: I8879900e57e1702d11797b81e86d0cc3f55bac22