csi: log fallthrough on invalid node IDs for client RPC (#7918)

When a CSI client RPC is given a specific node for a controller but
the lookup fails (because the node is gone or is an older version), we
fallthrough to select a node from all those available. This adds
logging to this case to aid in diagnostics.

nomad/client_csi_endpoint.go

@@ -134,6 +134,9 @@ func (a *ClientCSI) nodeForController(pluginID, nodeID string) (string, error) {
 		_, err = getNodeForRpc(snap, nodeID)
 		if err == nil {
 			return nodeID, nil
+		} else {
+			// we'll fall-through and select a node at random
+			a.logger.Trace("%s could not be used for client RPC: %v", nodeID, err)
 		}
 	}