Different tests were doing this in different ways. Centralize it all in
the base test class for functional tests. For both flavor and image, the
order of precedence is:
- Environment variables
- clouds.yaml configuration
- Guesswork (pick a cirros, Ubuntu or CentOS image for images, or the
flavor with the lowest RAM for flavors)
Change-Id: I90fda8ef48008c7fa634edc295c0e83e5f29387f
Signed-off-by: Stephen Finucane <stephenfin@redhat.com>
3244abd020