Extend LdapRealmTestCase to cover follow referral mode

This is a follow up to WFCORE-5936. Right now the LdapRealmTestCase just tests default referral-mode ignore in the dir-context. The idea is expanding the test (probably creating two different classes) for ignore and follow modes.

In my initial tests the apache directory server does not handle referrals OK in version 2.0.0-M24 used currently inside the tests. So probably this will also need an upgrade of apache directory dependencies to last version 2.0.0.AM26. It needs upgrade for the wildfly-core dependency to integrate fix for WFCORE-5936.