aws client setup refactor

[joelddiaz]

redo the parameters needed to set up an aws client (needed for other stuff i'm working on) so that it doesn't need to know about the internals of machinesetspec objects.

update controllers and tests using the aws client accordingly

[joelddiaz]

@csrwng i still need to test this once the machine object spec.roles[] changes are settled down, but could use a review on this at this point

[dgoodwin]

Still has a WIP tag, let me know if it's ok to merge.

[joelddiaz]

@dgoodwin i rebased and retested. things look good on my end. removed the WIP

[dgoodwin]

/lgtm