Often it is beneficial to use the functionality provided by `use_cirros`
and `cirros_deploy_image_upstream_url` to download and test with images
of other OS distributions. This patch changes the variable names to
reflect that use case.
`use_cirros` -> `download_custom_deploy_image`
`cirros_deploy_image_upstream_url` -> `custom_deploy_image_upstream_url`
The functionality of the old variables is retained for backwards
compatability.
Co-Authored-By: Alex Welsh <alex@stackhpc.com>
Change-Id: I8b3a973bd5ef19333af563c170b2a28fbbfb5c76
a6ce283146