Rolling updater enhancements

Add an UpdateAcceptor interface to the rolling updater which supports
injecting code to validate the first replica during scale-up. If the
replica is not accepted, the deployment fails. This facilitates canary
checking so that many broken replicas aren't rolled out during an update.

Make the rolling update scale amount configurable as a percent of the replica
count; a negative value changes the scale direction to down/up to support
in-place deployments.

pkg/kubectl/cmd/rollingupdate.go

@@ -258,13 +258,14 @@ func RunRollingUpdate(f *cmdutil.Factory, out io.Writer, cmd *cobra.Command, arg
 		updateCleanupPolicy = kubectl.RenameRollingUpdateCleanupPolicy
 	}
 	config := &kubectl.RollingUpdaterConfig{
-		Out:           out,
-		OldRc:         oldRc,
-		NewRc:         newRc,
-		UpdatePeriod:  period,
-		Interval:      interval,
-		Timeout:       timeout,
-		CleanupPolicy: updateCleanupPolicy,
+		Out:            out,
+		OldRc:          oldRc,
+		NewRc:          newRc,
+		UpdatePeriod:   period,
+		Interval:       interval,
+		Timeout:        timeout,
+		CleanupPolicy:  updateCleanupPolicy,
+		UpdateAcceptor: kubectl.DefaultUpdateAcceptor,
 	}
 	if cmdutil.GetFlagBool(cmd, "rollback") {
 		kubectl.AbortRollingUpdate(config)