Apply Google VM labels also to attached disks

drivers/google/compute_util.go

@@ -386,6 +386,7 @@ func (c *ComputeUtil) createInstance(d *Driver) error {
 			// The maximum supported disk size is 1000GB, the cast should be fine.
 			DiskSizeGb: int64(d.DiskSize),
 			DiskType:   c.diskType(),
+			Labels:     parseLabels(d),
 		}
 	} else {
 		instance.Disks[0].Source = c.zoneURL + "/disks/" + c.instanceName + "-disk"

drivers/google/google.go

@@ -227,7 +227,7 @@ func (d *Driver) GetCreateFlags() []mcnflag.Flag {
 		},
 		mcnflag.StringSliceFlag{
 			Name:  "google-label",
-			Usage: "Label to set on the VM (format: key:value). Repeat the flag to set more labels",
+			Usage: "Label to set on the VM and its disks (format: key:value). Repeat the flag to set more labels",
 		},
 		mcnflag.StringSliceFlag{
 			Name:  "google-metadata",