* Janitor: new docker-cleanup image version
The initial motivation for this version bump is support for docker 1.9+
Currently volumes don't get removed properly and lead to containers to
stall at start up, which is a pain to diagnose in rancher.
ref: https://github.com/meltwater/docker-cleanup/issues/24
* janitor: add support for KEEP_CONTAINERS_NAMED feature
* janitor: document '**None**' and '**All**'
* janitor: run with privileged mode unconditionnally
According to @sshipway, it seemed to be incompatible with a lot of
docker/rancher versions.
* janitor: bump docker-cleanup image version to 1.8.0
