Flatten action commands

[AlexisBruemmer]

Flatten and rename action commands:

juju action do --> juju run-action
juju action defined --> juju list-actions
juju action fetch --> juju show-action-output
juju action status --> juju show-action-status

(Review request: http://reviews.vapour.ws/r/4580/)

[AlexisBruemmer]

$$merge$$

[jujubot]

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