autoscaling_tag_def:  Raise ArgumentTypeErrors instead of ValueErrors
autoscaling_tag_def:  Raise ArgumentTypeErrors instead of ValueErrors

Raising ValueErrors for bad input instead of ArgumentTypeErrors was
causing argparse to mask relevant error messages.

Fixes TOOLS-318

vasiliykochergin/euca2ools,nagyistoce/euca2ools,nagyistoce/euca2ools,jhajek/euca2ools,vasiliykochergin/euca2ools,gholms/euca2ools,jhajek/euca2ools,gholms/euca2ools