chroot: add default user to the input group
chroot: add default user to the input group

fixes: https://github.com/beagleboard/Latest-Images/issues/29
Signed-off-by: Robert Nelson <d6c41255011d14bfa93d8562b946ca186cfa0c7b@gmail.com>

RobertCNelson/omap-image-builder,beagleboard/image-builder,beagleboard/image-builder,RobertCNelson/omap-image-builder