Add config_drive and user_data support to autoscale

This pull request adds support for `user_data` and `config_drive` to autoscale.  Although not explicitly documented in the autoscale API documentation it is indeed accepted.

In addition to this change, there is a small bugfix with updating the launch config, where if `key_name` was set, the body was incorrectly updated causing the API to respond with a 400.