Add new pwpolicy objectclass to test_xmprpc/objectclasses.py
    
    This defines the expected set of objectclasses in the XMLRPC
    tests.
    
    https://pagure.io/freeipa/issue/6964
    https://pagure.io/freeipa/issue/5948
    https://pagure.io/freeipa/issue/2445
    https://pagure.io/freeipa/issue/298
    
    Signed-off-by: Rob Crittenden <rcritten@redhat.com>
    Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>
    Reviewed-By: Christian Heimes <cheimes@redhat.com>
    Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>
    Reviewed-By: Christian Heimes <cheimes@redhat.com>