Move manager and worker nodes into the repository

[thojkooi]

• Support exposing the Docker Remote API using TLS when certificates are provided
• Add support for setting availability of the manager nodes on provisioning
• Add timeout to docker join and docker leave commands. Avoid long waiting time in case a host cannot be reached
• Add docker leave command when destroying a manager node, allows for down-scaling the amount of managers
• Fix some issues with docker join bash scripting
• Improve scripts to join worker nodes to cluster
• Remove need to pass do_token variable. Now instead uses the provider passed to the module
• Move manager and worker modules into a single repository, in the modules directory