Support habitat exported docker images

[drnic]

https://www.habitat.sh/ can export Docker images, which in turn docker_manager.rb could run.

Except @bodymindarts annoyingly tells me that we can't pass in simple env vars -e REDIS_PASSWORD=2134jfdjhaf into habitat containers. Instead we pass in -e HAB_REDIS='username="admin", password="adsfasdfsadf", db_name="adsfsadfdfsg"'

So to support habitat, we could keep the REDIS_PASSWORD concepts for configuration, but just change what env var is created (one HAB_REDIS instead of many REDIS_PASSWORD etc.

Proposal, cargo cult docker_manager.rb into habitat_docker_manager.rb (and _spec.rb) to support habitat