The busybox adduser and addgroup commands are ignored by docker,
as it avoids symlinks, but they are not compatible so this is
kind of a good idea.
See https://github.com/docker/docker/blob/master/pkg/idtools/usergroupadd_linux.go
However, these do not yet deal with creating mapping ranges in /etc/subuid and
/etc/subgid, so initially we provide a set that match the default docker name
so at least docker daemon --userns-remap=default should work.
Signed-off-by: Justin Cormack <justin.cormack@docker.com>
