Ensure password login possible when SSH_ROOT_PASSWORD is set

I have added a couple of lines that ensures password login being possible when SSH_ROOT_PASSWORD has been set.

The reason for not adding to end of sshd_config as proposed is due to any Match blocks that could be used in sshd_config needs to be at the very end of the file - thus only a complete in-place line substitution should be done (and looks cleaner as well).

Info on Match blocks: http://unix.stackexchange.com/questions/67334/openssh-how-to-end-a-match-block