Sync marks

This pr is only created to allow easier code review.

There is a remaining issue with offline nodes, but I have a fix in mind and will update the pull request today.

- Nodes that are currently offline are also included in the cluster nodes count. But those nodes won't ever transition to finished, and the waiting method will always time out. Does not happen when all nodes are online.

- Draft for a fix: evaluate node online status as crowbar does. Alter node count accordingly. I'd prefer to have the online status as part of the node attributes stored on the server and set by crowbar. This should get implemented later.