dotcloud/docker — pull request #1498 by moretea (2013-08-11 19:19:16+00:00)
Title: Do not overwrite env vars. Closes#1493

Issue #1493 describes that setting the ```HOME``` env var in a Dockerfile doesn't work.
I've verified this issue, and created a fix.

I also took the liberty to extend another test to make sure that non-default env vars still work, and to apply the fix for the ```HOME``` env var at the ```PATH```, ```container``` and ```HOSTNAME``` vars.