Wipe PID and ConmonPID in state after container stops

Matches the behavior of Docker.

Signed-off-by: Matthew Heon <matthew.heon@pm.me>

libpod/container_internal.go

@@ -1044,6 +1044,8 @@ func (c *Container) stop(timeout uint) error {
 		return err
 	}
 
+	c.state.PID = 0
+	c.state.ConmonPID = 0
 	c.state.StoppedByUser = true
 	if err := c.save(); err != nil {
 		return errors.Wrapf(err, "error saving container %s state after stopping", c.ID())