nri: add experimental NRI plugin.

Add a common NRI 'service' plugin. It takes care of relaying
requests and respones to and from NRI (external NRI plugins)
and the high-level containerd namespace-independent logic of
applying NRI container adjustments and updates to actual CRI
and other containers.

The namespace-dependent details of the necessary container
manipulation operations are to be implemented by namespace-
specific adaptations. This NRI plugin defines the API which
such adaptations need to implement.

Signed-off-by: Krisztian Litkey <krisztian.litkey@intel.com>

vendor/github.com/opencontainers/runtime-tools/validate/capabilities/validate.go

@@ -0,0 +1,31 @@
+package capabilities
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/syndtr/gocapability/capability"
+)
+
+// CapValid checks whether a capability is valid
+func CapValid(c string, hostSpecific bool) error {
+	isValid := false
+
+	if !strings.HasPrefix(c, "CAP_") {
+		return fmt.Errorf("capability %s must start with CAP_", c)
+	}
+	for _, cap := range capability.List() {
+		if c == fmt.Sprintf("CAP_%s", strings.ToUpper(cap.String())) {
+			if hostSpecific && cap > LastCap() {
+				return fmt.Errorf("%s is not supported on the current host", c)
+			}
+			isValid = true
+			break
+		}
+	}
+
+	if !isValid {
+		return fmt.Errorf("invalid capability: %s", c)
+	}
+	return nil
+}