cri: support blockio class in pod and container annotations

This patch adds support for a container annotation and two separate
pod annotations for controlling the blockio class of containers.

The container annotation can be used by a CRI client:
  "io.kubernetes.cri.blockio-class"

Pod annotations specify the blockio class in the K8s pod spec level:
  "blockio.resources.beta.kubernetes.io/pod"
  (pod-wide default for all containers within)

  "blockio.resources.beta.kubernetes.io/container.<container_name>"
  (container-specific overrides)

Correspondingly, this patch adds support for --blockio-class and
--blockio-config-file to ctr, too.

This implementation follows the resource class annotation pattern
introduced in RDT and merged in commit 893701220.

Signed-off-by: Antti Kervinen <antti.kervinen@intel.com>

cmd/ctr/commands/commands.go

@@ -189,6 +189,14 @@ var (
 			Name:  "apparmor-profile",
 			Usage: "enable AppArmor with an existing custom profile",
 		},
+		cli.StringFlag{
+			Name:  "blockio-config-file",
+			Usage: "file path to blockio class definitions. By default class definitions are not loaded.",
+		},
+		cli.StringFlag{
+			Name:  "blockio-class",
+			Usage: "name of the blockio class to associate the container with",
+		},
 		cli.StringFlag{
 			Name:  "rdt-class",
 			Usage: "name of the RDT class to associate the container with. Specifies a Class of Service (CLOS) for cache and memory bandwidth management.",