ActionComplete / ActionFailed called after Action completion

The worker now calls ActionComplete or ActionFailed on state, depending
on the success state of the Action and any errors.

The hook is set to an error state if the Action hook is missing, or if
other errors take place during hook execution.  If the Action hook sets
a fail state, the Hook will not error, rather the Action will fail.

DEPENDS: https://github.com/juju/juju/pull/527
I would agree but it will be implemented in the next PR if I don't implement it here, so I thought it pointless to implement the fail case a different way in this PR than in the next.