This happens when a new SAML or LDAP user signs up and it is not yet
created in cartodb. It results in a sync call to Central HTTP API.
This avoids such call when the Central api is not enabled (notably in
on-premise installations).
Also this fixes tests that otherwise wait forever on an `until`.
::User.any_instance.stubs(:create_in_central).raises('Error on state creating_user_in_central, mark_as_failure: false. Error: Application server responded with http 422: {"errors":["Existing username."]}')