Create /mnt/pass_through/<userid> in zygote if not created

Similar to /mnt/user, there is a very rare chance that the FUSE daemon
is started before vold mounts the volume, in that rare case, we should
still create the /mnt/pass_through/<userid> dir in zygote before bind
mounting into /storage

Test: manual
Bug: 135341433

Change-Id: Ibb0ee2657b3030ecec8fcef8e447f1fd4548457e