Make possible to send requests as anonymous users in integration tests

Until now requests always had "auth" headers either for an admin or a
regular user, depending on the value of "currentUser". Now, if
"currentUser" starts by "anonymous" no "auth" header is sent, which
makes possible to also test requests with users not logged in.

Signed-off-by: Daniel Calviño Sánchez <danxuliu@gmail.com>