action-fail: a jujuc command for Actions to set an error state

action-fail permits an Action to set an error value which will be returned to
the stateserver upon completion of the Action.  This does not prevent
action-set from adding more values to the results map.
action-fail: a jujuc command for Actions to set an error state

action-fail now uses the ActionFinish endpoint on State, so that any
values set in the action's result map will be handed back even in the
case of a failed Action.  The final call to action-fail will be the
message which is handed back along with the fail status.
action-fail: a jujuc command for Actions to set an error state

Final refactor of action-fail for action-set and actionFinish.
Merge pull request #868 from binary132/action-fail

jujuc action-fail

This is a re-open of https://github.com/juju/juju/pull/520 as the lander failed to see the script invocation.