Add ability to specify key profile

[cdodd]

This pull request adds the ability to specify which key pair profile to use when working with a stack. For reference see http://docs.aws.amazon.com/cli/latest/userguide/cli-chap-getting-started.html#cli-multiple-profiles. This allows you to work on stacks in different accounts without needing to manually switch out credential information.

This is optional, if key_profile is not specified in the stack then you will see the current behaviour, which is to use the default profile.

[cdodd]

I see the CircleCI checks are giving errors, but none of them are introduced by this pull request. I'm not clear on how previous CI tests have passed without these errors.

[acaire]

@cdodd Cheers for the pull request - Due to a newer version of flake8/pep8 by the looks, i'll investigate.

[acaire]

please rebase

[cdodd]

Done

[cdodd]

I rebased before https://github.com/cotdsa/cumulus/commit/7a38d2576f5e7a2b61b6adfada184f6b2414d0ce, I've now rebased again.

[acaire]

@cdodd apologies for the delay, I've been discussing the rewrite with @peterkh - Happy with this for now, although I think it's more appropriate that key_profile becomes boto_profile or similar.

It might also be worthwhile setting the param default to None and always passing boto_profile via the cloudformation.connect_to_region calls.