Better Peer handling for tasks

[pinges]

Description

Currently in PendingPeerRequest in getPeerToUse we are checking if the peer that was passed in is disconnected. If it is, we select another peer. That means that on the task level we cannot be sure which peer was used to do the task. It would be cleaner to fail if it is disconnected and handle that in the higher levels.

There can be two reasons for not being able to use a specific peer, a peer is disconnected, or it has too many ongoing requests.