Add allow_other mount option for appfuse.

After DocumentsProvider opens FD on app fuse, DocumentProvider passes it
to other applications. To allow other applications to use the FD on app
fuse, we need to specify allow_other mount option.

BUG=25756419

Change-Id: I3c729f90e5b822a7b1032bf80726cc234c0936b1
1 file changed