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>

docs/cri/config.md

@@ -143,6 +143,14 @@ version = 2
     # default_runtime_name is the default runtime name to use.
     default_runtime_name = "runc"
 
+    # ignore_blockio_not_enabled_errors disables blockio related
+    # errors when blockio support has not been enabled. By default,
+    # trying to set the blockio class of a container via annotations
+    # produces an error if blockio hasn't been enabled.  This config
+    # option practically enables a "soft" mode for blockio where these
+    # errors are ignored and the container gets no blockio class.
+    ignore_blockio_not_enabled_errors = false
+
     # ignore_rdt_not_enabled_errors disables RDT related errors when RDT
     # support has not been enabled. Intel RDT is a technology for cache and
     # memory bandwidth management. By default, trying to set the RDT class of