runtime: return hypervisor Pid in TaskExit event

Other RPC calls return Pid of hypervisor, the TaskExit should
return the same Pid.

Fixes: #1497

Signed-off-by: bin <bin@hyper.sh>

(backport https://github.com/kata-containers/kata-containers/pull/1498)
Signed-off-by: Francesco Giudici <fgiudici@redhat.com>
[ fix missing GetHypervisorPid method in MockSandbox ]
Signed-off-by: Peng Tao <bergwolf@hyper.sh>

src/runtime/containerd-shim-v2/utils.go

@@ -24,7 +24,7 @@ import (
 func cReap(s *service, status int, id, execid string, exitat time.Time) {
 	s.ec <- exit{
 		timestamp: exitat,
-		pid:       s.pid,
+		pid:       s.hpid,
 		status:    status,
 		id:        id,
 		execid:    execid,

src/runtime/virtcontainers/pkg/vcmock/sandbox.go

@@ -254,3 +254,7 @@ func (s *Sandbox) GetAgentURL() (string, error) {
 	}
 	return "", nil
 }
+
+func (s *Sandbox) GetHypervisorPid() (int, error) {
+	return 0, nil
+}