serverID to target remote leader or server

handle the case where we request a server-id which is this current server

update docs, error on node and server id params

more accurate names for tests

use shared no leader err, formatting

rm bad comment

remove redundant variable

command/agent/agent_endpoint.go

@@ -205,6 +205,11 @@ func (s *HTTPServer) AgentMonitor(resp http.ResponseWriter, req *http.Request) (
 		PlainText: plainText,
 	}
 
+	// if node and server were requested return error
+	if args.NodeID != "" && args.ServerID != "" {
+		return nil, CodedError(400, "Cannot target node and server simultaneously")
+	}
+
 	s.parse(resp, req, &args.QueryOptions.Region, &args.QueryOptions)
 
 	// Make the RPC