caddy-frontend: Publish only active slaves from main partition
As some of the nodes can lag behind, the system can be in state, that those nodes will send inactive (also destroyed) slave publish information. Before publishing it to master, check if each of slaves is really present on master.
Tasks:
- prove it really works on simulated environment
- check impact on massive simulated environment
- cover with a test (optionally)
- check test results with this change