gitlab-ci: Refactor code that show logs of failed acceptances

Replace the code (python) on after_script of the acceptance jobs that
is currently used to show the logs of failed tests. Instead it is used
the Avocado's testlogs plug-in which works likewise.

Signed-off-by: Wainer dos Santos Moschetta <wainersm@redhat.com>
Reviewed-by: Willian Rampazzo <willianr@redhat.com>
Message-Id: <20201211183827.915232-3-wainersm@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>