Check for asynchronous nodes in HA setups

[widhalmt]

In rare occasions the sync between nodes, esp. master nodes can break. If it breaks completely you see the nodes as disconnected but in even rarer occasions the sync continues but misses some objects.

e.g. you acknowledge a problem on one node but the other one misses the acknowledgement. This way you end up with an acknowledged problem but you might still get notifications for it.

We should find a way how to check if two nodes within a zone are synced completely.