touch /etc/motd if it does not exist.

/etc/motd file does not exist on the default
Ubuntu 14.04 EC2 image. This simply touches the
file if it doesn't exist before executing the
following `file.append` function.
"Note that if you just want to create a file and don't care about atime or mtime, you should use file.managed instead, as it is more feature-complete. (Just leave out the source/template/contents arguments, and it will just create the file and/or check its permissions, without messing with contents)"

I'm annoying - I know, but let's keep good patterns