Add test cases to verify LDAP caching on security realms.

The existing test cases are based on a statically defined set of LDIFs, testing of caching could consider a couple of options: -
1 - Interceptors within ApacheDS to verify if calls hit the directory.
2 - Updates to the directory that would affect the outcome of tests if there is a cache hit, tests can then be repeated with and without clearing the cache.

Note: It would be beneficial for this to use different users and groups and maybe even different partitions so that test ordering does not affect the outcome if changes are made to the directory.