Change AppFuse mount location to vold namespace

Previously, AppFuse is mounted in system_server's mount namespace. This
CL moves the mount location to vold namespace.

Relanding this since it fails to be merged on ag/5521004 (blocked by
Presubmit, seems to be caused by temporary state) - this one now
passes presubmit without any changes.

Bug: 110379912
Test: testOpenProxyFileDescriptor passes
Change-Id: Id93c26d5a98842c78f27850c83e15df619cec1ab
5 files changed