Fix storage cts due to app data storage isolation change

Now each apps storage data and obb are in its own process namespace,
apps will see it as another new mount point, which it always has write
access and not a normal mount point, so we need to fix the existing
tests to apply the new changes.

Bug: 183108201
Test: After turning on app data isolation change flag
atest android.appsecurity.cts.ExternalStorageHostTest#testExternalStorageNone29
atest android.appsecurity.cts.ExternalStorageHostTest#testExternalStorageRead29
atest android.appsecurity.cts.ExternalStorageHostTest#testExternalStorageWrite

Change-Id: I48a30bc554bb5d2966ed586bf02850820e888a46
4 files changed