Previously we would call `LazyUnbind` as soon
as proces starts. This does break `getcwd`
as it starts returning `(unreachable)`
due to mountpoint being gone from `chroot`.

This removes the need for `LazyUnbind` and
instead `unshare` mount namespace, making
the new process to have it's own mounts
that are not shared with parent process.
The mounts gets cleaned-up once the process
exists.