tests/acceptance: rename tests acceptance to tests avocado

tests/acceptance: rename tests acceptance to tests avocado

In the discussion about renaming the `tests/acceptance` [1], the
conclusion was that the folders inside `tests` are related to the
framework running the tests and not directly related to the type of
the tests.

This changes the folder to `tests/avocado` and adjusts the MAKEFILE, the
CI related files and the documentation.

[1] https://lists.gnu.org/archive/html/qemu-devel/2021-05/msg06553.html

Reviewed-by: Niek Linnenbank <nieklinnenbank@gmail.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Willian Rampazzo <willianr@redhat.com>
Message-Id: <20211105155354.154864-3-willianr@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>