bump version back to development status (0.9999)
docs: update image host command with -I,-m options

Using these options instead of -i and -n prevents an issue where the
default cluster template in the config may override these values if
master_instance_type and master_image_id are defined. This ensures the
user gets exactly the instance type and base AMI they are expecting when
launching the image host regardless of their config.

closes gh-388