Add docker volumes janitor

This cleans up tmp and logrotates /var/log every 12 hours.

Note that this janitor is separate from the box janitor because they
run as different users.

Fixes #503

setup/container/systemd/cloudron.target

@@ -2,8 +2,8 @@
 Description=Cloudron Smart Cloud
 Documentation=https://cloudron.io/documentation.html
 StopWhenUnneeded=true
-Requires=box.service janitor.timer
-After=box.service janitor.timer
+Requires=box.service janitor.timer docker_janitor.timer
+After=box.service janitor.timer docker_janitor.timer
 # AllowIsolate=yes
 
 [Install]

setup/container/systemd/docker_janitor.service

@@ -0,0 +1,14 @@
+[Unit]
+Description=Docker Volumes Janitor
+OnFailure=crashnotifier@%n.service
+
+[Service]
+Type=simple
+Restart=no
+ExecStart=/usr/sbin/docker_janitor
+KillMode=process
+User=root
+Group=root
+MemoryLimit=50M
+WatchdogSec=180
+

setup/container/systemd/docker_janitor.timer

@@ -0,0 +1,10 @@
+[Unit]
+Description=Docker Volumes Janitor
+StopWhenUnneeded=true
+
+[Timer]
+# this activates it immediately
+OnBootSec=0
+OnCalendar=*-*-* 0,6,12,18:00:00
+Unit=docker_janitor.service
+