ipatests: rpcclient now uses --use-kerberos=desired
    
    The integration tests are using rpcclient delivered
    by samba package. With samba 4.15, the options have
    been renamed and "--use-kerberos=desired" must be
    used instead of "-k".
    (see
    https://download.samba.org/pub/samba/rc/samba-4.15.0rc4.WHATSNEW.txt)
    
    Adapt the test to be compatible with both old and new versions.
    
    Fixes: https://pagure.io/freeipa/issue/8979
    Signed-off-by: Florence Blanc-Renaud <flo@redhat.com>
    Reviewed-By: Mohammad Rizwan <myusuf@redhat.com>