Refactor runtime events into Task* types

This removes the RuntimeEvent super proto with enums into separate
runtime event protos to be inline with the other events that are output
by containerd.

This also renames the runtime events into Task* events.

Fixes #1071

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

metrics/cgroups/cgroups.go

@@ -3,8 +3,6 @@
 package cgroups
 
 import (
-	"time"
-
 	"github.com/containerd/cgroups"
 	events "github.com/containerd/containerd/api/services/events/v1"
 	evt "github.com/containerd/containerd/events"
@@ -71,10 +69,7 @@ func (m *cgroupsMonitor) Stop(c runtime.Task) error {
 }
 
 func (m *cgroupsMonitor) trigger(id string, cg cgroups.Cgroup) {
-	if err := m.emitter.Post(m.context, &events.RuntimeEvent{
-		Timestamp:   time.Now(),
-		Type:        events.RuntimeEvent_OOM,
-		ID:          id,
+	if err := m.emitter.Post(m.context, &events.TaskOOM{
 		ContainerID: id,
 	}); err != nil {
 		log.G(m.context).WithError(err).Error("post OOM event")