Handle run action operation for terminated actions

[voidspace]

Fixes Bug #1534103.

Handle operations of kind RunAction where the action has terminated, by marking the action as failed.

To QA:

Bootstrap and deploy a charm with a long running action.
Trigger the action.
Whilst the action is running execute:
juju run --application APPNAME 'sudo shutdown -r now'

Fetch the output of the action. The action should be marked as failed.
There should be no log error lines saying " error: unknown operation kind run-action".

(Review request: http://reviews.vapour.ws/r/5667/)

[voidspace]

$$merge$$

[jujubot]

Status: merge request accepted. Url: http://juju-ci.vapour.ws:8080/job/github-merge-juju