Add a unit test for the LDAP cache layer
    
    This mostly confirms that when an entry is added, modified or
    deleted it is expunged from the cache.
    
    https://pagure.io/freeipa/issue/8798
    
    Signed-off-by: Rob Crittenden <rcritten@redhat.com>
    Reviewed-By: Rafael Guterres Jeffman <rjeffman@redhat.com>