Add subcommand prune to the container, volume, image and system commands

Signed-off-by: Kenfe-Mickael Laventure <mickael.laventure@gmail.com>
Upstream-commit: 280c8723667af385e0807a090ddc5cc57c46807e
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),
+		NewPruneCommand(dockerCli),
 	)
 	return cmd
 }