Acceptance Tests: move definition of distro checksums to the framework

Acceptance Tests: move definition of distro checksums to the framework

Instead of having, by default, the checksum in the tests, and the
definition of tests in the framework, let's keep them together.

A central definition for distributions is available, and it should
allow other known distros to be added more easily.

No behavior change is expected here, and tests can still define
a distro_checksum value if for some reason they want to override
the known distribution information.

Signed-off-by: Cleber Rosa <crosa@redhat.com>
Message-Id: <20210414221457.1653745-3-crosa@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Acked-by: Eric Auger <eric.auger@redhat.com>
[CR: split long lines]
Signed-off-by: Cleber Rosa <crosa@redhat.com>