Fix docker dev.

My last commit messed things up because it made it so every docker dev
instance would try to bind to port 8000 on the host machine.  After
the first one started, every other one would fail.

Changed it so only runserver binds to port 8000.  Also made bash.py
pass its command line args to docker, so you can add "-p 8000:8000" if
you want to use runserver while in the bash shell.