Leave support for legacy images

drivers/google/compute_util.go

@@ -459,6 +459,15 @@ func (c *ComputeUtil) uploadSSHKey(instance *raw.Instance, sshKeyPath string) er
 	metaDataValue := fmt.Sprintf("%s:%s %s\n", c.userName, strings.TrimSpace(string(sshKey)), c.userName)
 
 	metadata := instance.Metadata
+	// "sshKeys" was deprecated in favor of "ssh-keys" metadata key. However, old images may still depend
+	// on the old metadata configuration. And users may still have legitimate reasons to use these older
+	// images. As instance metadata is a simple key-value store, it should have no problems with having
+	// the keys defined twice under two different names. Legacy images will then still be able to use the
+	// legacy key naming, while new ones will get support for the expected new naming.
+	metadata.Items = append(metadata.Items, &raw.MetadataItems{
+		Key:   "sshKeys",
+		Value: &metaDataValue,
+	})
 	metadata.Items = append(metadata.Items, &raw.MetadataItems{
 		Key:   "ssh-keys",
 		Value: &metaDataValue,