[sudo-access] omnidoor security fix

[Jake]

daniel pointed out that the default username "debian" was enabled on the
beaglebone black at the front door computer, with the default password AND sudo
access.

since i think everyone is logging in as root anyway (which has a decent
password and most people probably use SSH keys anyway) i disabled the debian
account by changing its shell (in /etc/passwd) to /bin/false, and i also set
the password to something else anyway.

-jake