Add DOCKER_HOST env var for client

This env var will set the -H flag on the docker
client.
Update Dockerfile to use stackbrew/ubuntu (until it graduates), update Dockerfile MAINTAINER line, coalesce all apt-get installs into one invocation (including s3cmd by bringing in backports)
Minor fixes to the basic command documentation
Merge pull request #3344 from tianon/dockerfile-cleanup

Many various Dockerfile cleanups
Merge pull request #3395 from jamtur01/basicsfixes

Minor fixes to the basic command documentation
Merge pull request #3303 from crosbymichael/add-host-flag

Add DOCKER_HOST env var for client