Action results

*Action Results* in the State
==

An Action can now be `Fail()`'ed or `Complete()`'ed, and the relevant output will be stored in the `actionresults` collection in the juju db in mongo.

The reason, or the output will be written to the `ActionResult`, along with the details of the `Action`.

The prefix of the `ActionResult.Id()` will also encode the `Action.Id()` from which it was generated (which itself encodes the `Unit.globalKey()` that the `Action` was queued for.
Given the comments by @davecheney about not importing the errors package if the fmt package is already imported... should I still make this change?