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>

vendor/github.com/intel/goresctrl/pkg/cgroups/cgroupid.go

@@ -0,0 +1,65 @@
+package cgroups
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"sync"
+)
+
+// CgroupID implements mapping kernel cgroup IDs to cgroupfs paths with transparent caching.
+type CgroupID struct {
+	root  string
+	cache map[uint64]string
+	sync.Mutex
+}
+
+// NewCgroupID creates a new CgroupID map/cache.
+func NewCgroupID(root string) *CgroupID {
+	return &CgroupID{
+		root:  root,
+		cache: make(map[uint64]string),
+	}
+}
+
+// Find finds the path for the given cgroup id.
+func (cgid *CgroupID) Find(id uint64) (string, error) {
+	found := false
+	var p string
+
+	cgid.Lock()
+	defer cgid.Unlock()
+
+	if path, ok := cgid.cache[id]; ok {
+		return path, nil
+	}
+
+	err := fsi.Walk(cgid.root, func(path string, info os.FileInfo, err error) error {
+		if err != nil {
+			if os.IsNotExist(err) {
+				return nil
+			}
+			return err
+		}
+
+		if found {
+			return filepath.SkipDir
+		}
+
+		if info.IsDir() && id == getID(path) {
+			found = true
+			p = path
+			return filepath.SkipDir
+		}
+		return nil
+	})
+
+	if err != nil {
+		return "", err
+	} else if !found {
+		return "", fmt.Errorf("cgroupid %v not found", id)
+	} else {
+		cgid.cache[id] = p
+		return p, nil
+	}
+}