use state machine management for exec.Pid()

Signed-off-by: Lifubang <lifubang@acmcoder.com>

runtime/v1/linux/proc/deleted_state.go

@@ -69,3 +69,7 @@ func (s *deletedState) SetExited(status int) {
 func (s *deletedState) Exec(ctx context.Context, path string, r *ExecConfig) (proc.Process, error) {
 	return nil, errors.Errorf("cannot exec in a deleted state")
 }
+
+func (s *deletedState) Pid() int {
+	return -1
+}