Some fixes found while running through things.

Aids with cut-and-paste of instruction portions while reading along.
Don't diaf - just fix the authorized_keys file.
Make install-dependencies a little more proactive.
Change default location for the bootstrap image.

Non-world readable home dirs mean you need to put your image
somewhere. This is a demo/bootstrap process, so just put them there.
Fancy people can always choose something else.
demo runs on the bootstrap node.  Make this obvious.