Implement `HA mode` about hostercore HOT 1 OPEN

Additional list of requirements:

• vm migrate to automatically stop the VM, replicate it to a new endpoint, and start it there (can only be done on the candidate nodes)
• running api stop on a worker node, will trigger a graceful exit from the cluster for such a node (which means that it can be rebooted, or shutdown for maintenance without the cluster manager moving over it's VMs to other members)
• implement the SSL encryption to protect the communications between nodes (it will be optional, and mostly manual due to the fact that it will rely on the organisational standards that are already in place, eg manual vs automatic SSL Certificate management, internal CAs, etc)
• create the documentation on how to use an internal CA to sign the HTTP certificates and use them in the api to activate the SSL encryption mode between HA nodes
• restapi_config.json - #58

Done:

• api stop to automatically detect the HA mode, if the node where this command is executed belongs to a candidate group, then it will notify other cluster members to stop the HA mode, otherwise the command will fail asking user to run it on one of the candidate nodes
• api status to return production or debug HA mode within the status information
• restapi_config.json has been implemented
• vm migrate option has been dropped for now, because we will migrating from SSH to REST API for the most functions and it will slow down that project migration

Still to do:

• SSL/HTTPs integration/implementation
• Docs for the SSL/HTTPs
• worker's clean disconnect

from hostercore.