Add `Scope` field to Volume

Signed-off-by: Brian Goff <cpuguy83@gmail.com>

types/types.go

@@ -395,6 +395,7 @@ type Volume struct {
 	Mountpoint string                 // Mountpoint is the location on disk of the volume
 	Status     map[string]interface{} `json:",omitempty"` // Status provides low-level status information about the volume
 	Labels     map[string]string      // Labels is metadata specific to the volume
+	Scope      string                 // Scope describes the level at which the volume exists (e.g. `global` for cluster-wide or `local` for machine level)
 }
 
 // VolumesListResponse contains the response for the remote API: