Remove call to deprecated neterr.Temporary() method

lib/teleagent/agent.go

@@ -18,7 +18,6 @@ import (
 	"io"
 	"net"
 	"os"
-	"strings"
 	"time"
 
 	"github.com/gravitational/teleport/lib/utils"
@@ -98,11 +97,11 @@ func (a *AgentServer) Serve() error {
 			if !ok {
 				return trace.Wrap(err, "unknown error")
 			}
-			if !neterr.Temporary() {
-				if strings.Contains(neterr.Error(), "use of closed network connection") {
-					return nil
-				}
-				log.WithError(err).Error("Got permanent error.")
+			if utils.IsUseOfClosedNetworkError(neterr) {
+				return nil
+			}
+			if !neterr.Timeout() {
+				log.WithError(err).Error("Got non-timeout error.")
 				return trace.Wrap(err)
 			}
 			if tempDelay == 0 {
@@ -113,7 +112,7 @@ func (a *AgentServer) Serve() error {
 			if max := 1 * time.Second; tempDelay > max {
 				tempDelay = max
 			}
-			log.WithError(err).Errorf("Got temporary error (will sleep %v).", tempDelay)
+			log.WithError(err).Errorf("Got timeout error (will sleep %v).", tempDelay)
 			time.Sleep(tempDelay)
 			continue
 		}