fix(image): only use numerical IDs for label auto-completion (#865)

We currently use the deprecated `Get` method here. Instead we can just
parse an integer and use that as the ID, since you can only get or
update labels on images you can modify (snapshots and backups), which
only have numerical IDs and no names anyway.

internal/hcapi2/image.go

@@ -43,10 +43,14 @@ func (c *imageClient) Names() []string {
 	return names
 }
 
-// ImageLabelKeys returns a slice containing the keys of all labels assigned to
-// the Image with the passed idOrName.
-func (c *imageClient) LabelKeys(idOrName string) []string {
-	img, _, err := c.Get(context.Background(), idOrName)
+// LabelKeys returns a slice containing the keys of all labels assigned to
+// the Image with the passed id.
+func (c *imageClient) LabelKeys(id string) []string {
+	imgID, err := strconv.ParseInt(id, 10, 64)
+	if err != nil {
+		return nil
+	}
+	img, _, err := c.GetByID(context.Background(), imgID)
 	if err != nil || img == nil || len(img.Labels) == 0 {
 		return nil
 	}