fix(login) make redirect parameter optional (#622)

* If there is a redirect param in the request use it otherwise check if
there is a redirect URL
* update keycloak config test example to remove logout url

This means it is no longer needed to put redirect=false in the request
to log in using the API. But previous login requests with a redirect URL
will continue working as the redirect parameter is optional

Covers [BPO-655](https://bonitasoft.atlassian.net/browse/BPO-655)