feat(client/deis): add python3 support

Changes:
- use python future for single source
- change octals to new style of `0oXXX`
- add `future==0.14.1` as dependency

Breaking Changes:
- `future==0.14.1` requires python >= 2.6
In this case `future` is a python2/3 compatibility library we're using. (I had to Google this @bacongobbler, full disclosure.)

I think the fix is that `future==0.14.1` also needs to be added to the `tests/bin/build-client.sh` script and the `docs/docs_requirements.txt` pip manifest file. (We have the client requirements repeated in several places, which is lame--we should fix that.)