Actions CLI - tracer implementation

Just connects the command line 'actions' and 'do' to the apiserver; basic initial CLI implementation
Yeah, `juju do` is indeed a much cuter spelling than `juju action run`... but I'm still really thinking that `do` should just redirect to the canonical form.

(I'm imagining a future in which we manage a command line client with a nice clean set of top-level entity-focused commands -- `juju machine [add,remove,etc]`, `juju service [get,set,destroy,etc]` -- alongside a very few nice obvious shortcut verbs -- `juju deploy`, `juju scale`, `juju do`, `juju relate`.)