WFLY-1668 added TestCase for LdapExtLoginModule caching passwords

Tests for LdapExtLoginModule mechanism to cache passwords obtained from external sources.
https://issues.jboss.org/browse/JBQA-7995

Tests ignored, because of:
https://issues.jboss.org/browse/WFLY-1668
https://bugzilla.redhat.com/show_bug.cgi?id=982539