Don't raise Exception if no Docker containers are running, fix #980
Don't raise Exception if we fail to get some Docker croup info, fix #981
Minors improvements to Docker check logic and compatibility
Merge pull request #989 from DataDog/docker-less-exception

Less Exception with Docker check
Remove unused file
Merge branch 'master' of https://github.com/DataDog/dd-agent
Merge branch 'master' into v4.x