Avoid creating cookies per path

In commit fa3231c2, app.config['APPLICATION_ROOT'] was set to avoid sharing cookies between different instances of the application. However, if url_prefix is not set (empty) the default value '/' in app.config['APPLICATION_ROOT'] is overridden. This causes that each query to tests cases to store its own cookie leading to consume the space available for them and causing login issues.

Fix the issue by only override APPLICATION_ROOT if url_prefix is set.

Signed-off-by: Walter Lozano walter.lozano@collabora.com