Debian related defaults

I've changed two things:

- printmotd
  Default is no, since Debian's own motd handling
- host keys
  Default is: RSA, DSA and ECDSA

I'm still verifying when ECDSA became available on Ubuntu.

But what do you think about the changes?
Instead of using `<` we should have explicit support for Ubuntu 14.04 and Debian 7, just like the other supported versions and list them in the README and the metadata.json