Improve the use-local/aws flows

[JoshBroomberg]

use-local/use-aws probably should not set the home directory. Consider better mechanisms for this.

It is too easy to use-local in one place then switch locations and continue operating on the wrong local directory. There is also a weird state gap if use-local is not called when stop-aws is called but calling use-local during this process seems wrong as it sets the call location as the new home.

Maybe a set-home command which can also be used to blank out the home field during aws teardown.

[JoshBroomberg]

Consider having a variable for running and the kind of run (local/aws). Then allow separate control over the home directory with restarts based on the state of running.