Removes the test database if the build fails

Sometime the test database is not destroyed because the build is
interrupted by an uncaught error. This causes an error during the next
build.

.gitlab-ci.yml

@@ -38,3 +38,12 @@ test:
     stage: test
     script:
         - python manage.py test
+
+cleanup:
+    stage: cleanup
+    script:
+        # If an uncaught error occurs, the test database has to be destroyed
+        # manually
+        - mysql --user=root --password="$MYSQL_ROOT_PASSWORD" --host="$DBHOST"
+            -e "DROP DATABASE test_$DBNAME" || true
+    when: on_failure