runc-shim: only defer init process exits

In order to make sure that we don't publish task exit events for init
processes before we do for execs in that container, we added logic to
`processExits` in 892dc54 to skip these
and let the pending exec's `handleStarted` closure process them.

However, the conditional logic in `processExits` added was faulty - we
should only defer processing of exit events related to init processes,
not other execs. Due to this missing condition,
892dc54 introduced a bug where, if
there are many concurrent execs for the same container/init pid, exec
exits are skipped and then never published, resulting in hanging
clients.

This commit adds the missing logic to `processExits`.

Signed-off-by: Laura Brehm <laurabrehm@hey.com>
(cherry picked from commit 6d00c3a)
Signed-off-by: Laura Brehm <laurabrehm@hey.com>

runtime/v2/runc/task/service.go

@@ -677,7 +677,8 @@ func (s *service) processExits() {
 		// process.
 		var cps, skipped []containerProcess
 		for _, cp := range s.running[e.Pid] {
-			if s.pendingExecs[cp.Container] != 0 {
+			_, init := cp.Process.(*process.Init)
+			if init && s.pendingExecs[cp.Container] != 0 {
 				// This exit relates to a container for which we have pending execs. In
 				// order to ensure order between execs and the init process for a given
 				// container, skip processing this exit here and let the `handleStarted`