Add new df subcomand to the system command

This command display the state of the data usage of the docker daemon.

Signed-off-by: Kenfe-Mickael Laventure <mickael.laventure@gmail.com>
Upstream-commit: b650a7bd27dcdbb4cddbfdc2cf62f41b5a8e8652
Component: engine

components/engine/cli/command/system/cmd.go

@@ -22,6 +22,7 @@ func NewSystemCommand(dockerCli *command.DockerCli) *cobra.Command {
 	cmd.AddCommand(
 		NewEventsCommand(dockerCli),
 		NewInfoCommand(dockerCli),
+		NewDiskUsageCommand(dockerCli),
 		NewPruneCommand(dockerCli),
 	)
 	return cmd