docker-inspect: Extend docker inspect to export image/container metadata related to graph driver

Export image/container metadata stored in graph driver. Right now 3 fields
DeviceId, DeviceSize and DeviceName are being exported from devicemapper.
Other graph drivers can export fields as they see fit.

This data can be used to mount the thin device outside of docker and tools
can look into image/container and do some kind of inspection.

Signed-off-by: Vivek Goyal <vgoyal@redhat.com>

api/types/types.go

@@ -75,6 +75,11 @@ type Image struct {
 	Labels      map[string]string
 }
 
+type GraphDriverData struct {
+	Name string
+	Data map[string]string
+}
+
 // GET "/images/{name:.*}/json"
 type ImageInspect struct {
 	Id              string
@@ -90,6 +95,7 @@ type ImageInspect struct {
 	Os              string
 	Size            int64
 	VirtualSize     int64
+	GraphDriver     GraphDriverData
 }
 
 // GET  "/containers/json"
@@ -218,6 +224,7 @@ type ContainerJSONBase struct {
 	AppArmorProfile string
 	ExecIDs         []string
 	HostConfig      *runconfig.HostConfig
+	GraphDriver     GraphDriverData
 }
 
 type ContainerJSON struct {