feat(client): add proxy support

Added proxy support via environment variables.
docs(using_deis): clean up proxy support
Merge pull request #1634 from carmstrong/client_proxy_support

feat(client): add proxy support
feat(*): add `make test-style` targets

This gives us an opporunity to run code checkers and linters as part
of testing, as we used to on travis-ci.org. By default, unit tests
will check code syntax and style first.
ref(*): clean up Go and Python code for `make test-style`