cmd/dist, cmd/ctr: move image store access to GRPC

With this changeset, image store access is now moved to completely
accessible over GRPC. No clients manipulate the image store database
directly and the GRPC client is fully featured. The metadata database is
now managed by the daemon and access coordinated via services.

Signed-off-by: Stephen J Day <stephen.day@docker.com>

services/content/service.go

@@ -38,7 +38,7 @@ func init() {
 
 func NewService(ic *plugin.InitContext) (interface{}, error) {
 	return &Service{
-		store: ic.Store,
+		store: ic.Content,
 	}, nil
 }
 

services/rootfs/service.go

@@ -22,7 +22,7 @@ func init() {
 	plugin.Register("rootfs-grpc", &plugin.Registration{
 		Type: plugin.GRPCPlugin,
 		Init: func(ic *plugin.InitContext) (interface{}, error) {
-			return NewService(ic.Store, ic.Snapshotter)
+			return NewService(ic.Content, ic.Snapshotter)
 		},
 	})
 }