Revert "root default password to boot2docker"

This reverts commit 1e1e1deea4485a703443f5660ace51205f9faa20.
using user docker

user docker is created by tinycore on boot when "user=docker" is add to
append in boot config
Revert "using user docker"

This reverts commit caec0dbe5cfda064de0f5f8f25fb72ab06729a8e.