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/3/docker-compose.yml

@@ -0,0 +1,20 @@
+cleanup:
+  image: meltwater/docker-cleanup:1.8.0
+  environment:
+    CLEAN_PERIOD: ${FREQUENCY}
+    DELAY_TIME: "900"
+    KEEP_IMAGES: "${KEEP}"
+    KEEP_CONTAINERS: "${KEEPC}"
+    KEEP_CONTAINERS_NAMED: "${KEEPCN}"
+    LOOP: "true"
+    DEBUG: "0"
+  labels:
+     io.rancher.scheduler.global: "true"
+     io.rancher.scheduler.affinity:host_label_ne: "${EXCLUDE_LABEL}"
+  net: none
+  privileged: true
+  tty: false
+  stdin_open: false
+  volumes:
+    - /var/run/docker.sock:/var/run/docker.sock
+    - /var/lib/docker:/var/lib/docker