Implement task update

This allows tasks to have their resources updated as they are running.

Fixes #1067

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

spec_unix.go

@@ -11,6 +11,7 @@ import (
 	"strings"
 
 	"github.com/containerd/containerd/api/services/containers/v1"
+	"github.com/containerd/containerd/api/services/tasks/v1"
 	"github.com/containerd/containerd/images"
 	protobuf "github.com/gogo/protobuf/types"
 	"github.com/opencontainers/image-spec/specs-go/v1"
@@ -290,3 +291,17 @@ func WithSpec(spec *specs.Spec) NewContainerOpts {
 		return nil
 	}
 }
+
+func WithResources(resources *specs.LinuxResources) UpdateTaskOpts {
+	return func(ctx context.Context, client *Client, r *tasks.UpdateTaskRequest) error {
+		data, err := json.Marshal(resources)
+		if err != nil {
+			return err
+		}
+		r.Resources = &protobuf.Any{
+			TypeUrl: specs.Version,
+			Value:   data,
+		}
+		return nil
+	}
+}