This disables the slow_chown feature (nobody in their right mind
is going to be choosing erofs and want to slowly chown each file),
indicates that we support idmaps if the kernel supports it, and makes
sure to chown the upperdir.
This is more or less exactly how the overlay snapshotter does things,
minus the slow_chown part (which has discussions about dropping
altogether at some point anyways).
Signed-off-by: Andrew Halaney <ahalaney@netflix.com>