Capture stack images

Provides the gonzo commands / options:
``gonzo image-create <instance-name> <image-name>``
``gonzo image-delete <image-name>``
``gonzo stack-launch [--create-images] [--quiet] [--delete-after-complete]``

The intention is to use the latter to capture images of long stack builds overnight, and then use the images for fast stack builds during the day.