Discovery: UnicastZenPing - use temporary node ids if can't resolve node by it's address

The Unicast Zen Ping mechanism is configured to ping certain host:port combinations in order to discover other node. Since this is only a ping, we do not setup a full connection but rather do a light connect with one channel. This light connection is closed at the end of the pinging.

During pinging, we may discover disco nodes which are not yet connected (via temporalResponses). UnicastZenPing will setup the same light connection for those node. However, during pinging a cluster state may arrive with those nodes in it. In that case , we will mistakenly believe those nodes are connected and at the end of pinging we will mistakenly disconnect those valid node.

This commit makes sure that all nodes UnicastZenPing connects to have a unique id and can be safely disconnected.

Closes #7719