Update ctr containers and tasks command

This moves container and tasks commands under the containers and tasks
top level commands.

Signed-off-by: Michael Crosby <crosbymichael@gmail.com>

cmd/ctr/kill.go

@@ -5,7 +5,7 @@ import (
 	"github.com/urfave/cli"
 )
 
-var killCommand = cli.Command{
+var taskKillCommand = cli.Command{
 	Name:      "kill",
 	Usage:     "signal a container (default: SIGTERM)",
 	ArgsUsage: "CONTAINER",