New relic support

Introduce two new environment configuration variables: NEW_RELIC_INI and NEW_RELIC_STAGE
Added new extra "newrelic" installation opt-in.

Docker-DCO-1.1-Signed-off-by: Olivier Gambier <olivier@docker.com> (github: dmp42)
Removing dotcloud related stuff

Docker-DCO-1.1-Signed-off-by: Olivier Gambier <olivier@docker.com> (github: dmp42)
Cleanup

Removed no more existing package and adding missing on.
Upped cover-min to what we currently have (67%).

Docker-DCO-1.1-Signed-off-by: Olivier Gambier <olivier@docker.com> (github: dmp42)
Loose dev requirements

Docker-DCO-1.1-Signed-off-by: Olivier Gambier <olivier@docker.com> (github: dmp42)
Python compat

Docker-DCO-1.1-Signed-off-by: Olivier Gambier <olivier@docker.com> (github: dmp42)
Updated changelog to prepare 0.8 release

Docker-DCO-1.1-Signed-off-by: Olivier Gambier <olivier@docker.com> (github: dmp42)
Amending previous commits

- don't source NEW_RELIC_INI multiple times
- better variable name for new relic ini ref
- learn to stop worrying about dev dependencies
- trailing coma in extras section of setup to avoid changing multiple lines when adding a new one

Docker-DCO-1.1-Signed-off-by: Olivier Gambier <olivier@docker.com> (github: dmp42)
Merge pull request #514 from docker/next-release

Preparing 0.8