weed/shell: support -noLock flag in volumeServer.evacuate (#12501) (#12516)

* weed/shell: support -noLock flag in volumeServer.evacuate (#12501)

* shell: return flag parse errors from volumeServer.evacuate

A typo such as -noLock=invalid printed the parse error but the command
still succeeded, so a piped script treated the evacuation as done.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

* shell: volumeServer.evacuate -h prints usage without failing

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

---------

Co-authored-by: Chris Lu <chrislusf@users.noreply.github.com>
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

weed/shell/command_volume_server_evacuate.go

@@ -2,6 +2,7 @@ package shell
 
 import (
 	"cmp"
+	"errors"
 	"flag"
 	"fmt"
 	"io"
@@ -43,6 +44,7 @@ func (c *commandVolumeServerEvacuate) Help() string {
 	good destination to meet the replication requirement. 
 	E.g. a volume replication 001 in a cluster with 2 volume servers can not be moved.
 	You can use "-skipNonMoveable" to move the rest volumes.
+	You can use "-noLock" to run without cluster-wide lock.
 
 `
 }
@@ -62,14 +64,20 @@ func (c *commandVolumeServerEvacuate) Do(args []string, commandEnv *CommandEnv,
 	// TODO: remove this alias
 	applyChangeAlias := vsEvacuateCommand.Bool("force", false, "actually apply the changes (alias for -apply)")
 	retryCount := vsEvacuateCommand.Int("retry", 0, "how many times to retry")
+	noLock := vsEvacuateCommand.Bool("noLock", false, "do not lock the admin shell at one's own risk")
 	if err = vsEvacuateCommand.Parse(args); err != nil {
-		return nil
+		if errors.Is(err, flag.ErrHelp) {
+			return nil
+		}
+		return err
 	}
 
 	handleDeprecatedForceFlag(writer, vsEvacuateCommand, applyChangeAlias, applyChange)
 	infoAboutSimulationMode(writer, *applyChange, "-apply")
 
-	if err = commandEnv.confirmIsLocked(args); err != nil && *applyChange {
+	if *noLock {
+		commandEnv.SetNoLock(true)
+	} else if err = commandEnv.confirmIsLocked(args); err != nil && *applyChange {
 		return
 	}
 	if *volumeServer == "" && *c.volumeRack == "" {