upgrade janitor to latest image version, docker 1.9+ support (#154)

* 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

templates/janitor/README.md

@@ -15,13 +15,13 @@ that are taking up space; note that this may not be what you want if you
 are using stopped containers to hold volumes!  If this is the case, use the
 Keep List below.
 
-This cleanup will help to prevent the /var/lib/docker filesystem from filling 
+This cleanup will help to prevent the /var/lib/docker filesystem from filling
 up with old and unused container images, which is an issue on lighter-weight
 Docker hosts.
 
 ### Keep list
 
-You can specify match patterns for unused Images, and stopped Containers, 
+You can specify match patterns for unused Images, and stopped Containers,
 which should be excluded from the cleanup.
 
 The match patterns are comma-separated Left Anchored Bash Shell wildcard
@@ -40,9 +40,11 @@ However it will not match
 * bar:latest
 * foo/\*:v1
 
-By default, nothing will be matched.  If you want to match everything, 
+By default, nothing will be matched.  If you want to match everything,
 then use a pattern **\*:\***
 
+The self-descriptive values '\*\*None\*\*' and '\*\*All\*\*' can also be used.
+
 ### Warning
 
 If you are using 'run-once' sidekick containers that mount a volume, then