tests/Makefile: allow control over tags during check-acceptance

tests/Makefile: allow control over tags during check-acceptance

Although it is possible to run a specific test using the avocado
command-line, a user may want to use a specific tag while running the
``make check-acceptance`` during the development or debugging.

This allows using the AVOCADO_TAGS environment variable where the user
takes total control of which tests should run based on the tags defined.

This also makes the check-acceptance command flexible to restrict tests
based on tags while running on CI.

e.g.:

AVOCADO_TAGS="foo bar baz" make check-acceptance

Signed-off-by: Willian Rampazzo <willianr@redhat.com>
Tested-by: Wainer dos Santos Moschetta <wainersm@redhat.com>
Reviewed-by: Wainer dos Santos Moschetta <wainersm@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20210923161141.232208-2-willianr@redhat.com>