cmd/list: Rename a variable for ease of grepping

It's better to avoid single letter variables in general, because they
are so hard to grep for.

This will make the subsequent commit easier to read.

https://github.com/containers/toolbox/pull/1190

src/cmd/list.go

@@ -302,7 +302,7 @@ func listOutput(images []toolboxImage, containers []toolboxContainer) {
 	}
 }
 
-func (i *toolboxImage) UnmarshalJSON(data []byte) error {
+func (image *toolboxImage) UnmarshalJSON(data []byte) error {
 	var raw struct {
 		ID      string
 		Names   []string
@@ -314,19 +314,19 @@ func (i *toolboxImage) UnmarshalJSON(data []byte) error {
 		return err
 	}
 
-	i.ID = raw.ID
-	i.Names = raw.Names
+	image.ID = raw.ID
+	image.Names = raw.Names
 	// Until Podman 2.0.x the field 'Created' held a human-readable string in
 	// format "5 minutes ago". Since Podman 2.1 the field holds an integer with
 	// Unix time. Go interprets numbers in JSON as float64.
 	switch value := raw.Created.(type) {
 	case string:
-		i.Created = value
+		image.Created = value
 	case float64:
-		i.Created = utils.HumanDuration(int64(value))
+		image.Created = utils.HumanDuration(int64(value))
 	}
 
-	i.Labels = raw.Labels
+	image.Labels = raw.Labels
 
 	return nil
 }