Adding support for android-automotive image

Hi,
it looks like this project can not support system image of Android Automotive now.
It throws following exception, when the system image is for Android Automotive.
Traceback (most recent call last):
File "/home/jou1/Development/android-emulator-container-scripts/venv/bin/emu-docker", line 33, in
sys.exit(load_entry_point('emu-docker', 'console_scripts', 'emu-docker')())
File "/home/jou1/Development/android-emulator-container-scripts/emu/emu_docker.py", line 300, in main
args.func(args)
File "/home/jou1/Development/android-emulator-container-scripts/emu/emu_docker.py", line 87, in create_docker_image
sys_docker = SystemImageContainer(img, args.repo)
File "/home/jou1/Development/android-emulator-container-scripts/emu/containers/system_image_container.py", line 34, in __init__
self.system_image_zip = SystemImageReleaseZip(sort)
File "/home/jou1/Development/android-emulator-container-scripts/emu/android_release_zip.py", line 128, in __init__
self.props["qemu.short_tag"] = self.short_tag()
File "/home/jou1/Development/android-emulator-container-scripts/emu/android_release_zip.py", line 168, in short_tag
return self.SHORT_TAG[self.tag()]
KeyError: 'android-automotive'