Add environment vehicle

[WENJZ18]

Thanks for your well-done job! I try to add some environment vehicles and set them autopilot, but all of them don't move in synchronous_mode while training . I have tried this in carla 0.9.6(without traffic manager) and carla 0.9.8(with traffic manager), neither of which work. I wonder if you have tried this before or know how to solve this problem? Thanks a lot.