AWSBoxen deployment tweaks

(Not ready for merge; just looking for feedback)

I've started to take a look at the deployment setup here, and have made some tweaks to .awsboxen.json based on my latest experiments in awsboxen.  Changes:

  * Pass in the database password as a parameter, like "awsboxen deploy -D DBPassword=blah stack-name"
  * Optional prefix for the DNS names, so we can all do trial deploys without clobbering each other
  * Use my experimental "UserDataFiles" helper function to clean up the config file stuff

The "UserDataFiles" is something I just whipped up, and is only on awsboxen trunk.  It lets you specify a hash where the keys are filenames, and the values are what gets JSON-serialized into the file at launch time.  Basically it's a little pre-processor that produces the UserData shell script automatically.

What do you think about the approach?  If it seems sensible then I'll clean up the implementation, document and release it.