docs(platform_monitoring): make cAdvisor unit more resilient

fixes #3221

Author: haf

docs/managing_deis/platform_monitoring.rst

@@ -43,7 +43,11 @@ To run cAdvisor on all hosts in the cluster, you can submit and start a fleet se
 
     [Service]
     ExecStartPre=/bin/sh -c "docker history google/cadvisor:latest >/dev/null || docker pull google/cadvisor:latest"
+    ExecStartPre=/bin/sh -c "docker inspect cadvisor >/dev/null && docker rm -f cadvisor || true"
     ExecStart=/usr/bin/docker run --volume=/:/rootfs:ro --volume=/var/run:/var/run:rw --volume=/sys:/sys:ro --volume=/var/lib/docker/:/var/lib/docker:ro --publish=8080:8080 --name=cadvisor google/cadvisor:latest
+    ExecStopPost=-/usr/bin/docker rm -f cadvisor
+    Restart=on-failure
+    RestartSec=5
 
     [Install]
     WantedBy=multi-user.target