Make container_monitor mechanism distributed

[Kexkey]

container_monitor is a docker-managed volume that is used to let other containers know about container's status. For example, the bitcoin container will write a file named bitcoin_ready on the volume to let other containers that it is ready. It is useful to sync tasks and wait for prerequisites.

Problem is when cyphernode runs in a Docker Swarm with distributed nodes, the volumes are not replicated throughout the nodes.

We need a sync mechanism that will work in a distributed deployment.