Py3: Fix vault tests
    
    * Bump PKI to 10.5.1-2, which fixes an issue with KRA under Python 3
    * Correct encoding of secret
    
    https://pagure.io/freeipa/issue/7033
    
    Signed-off-by: Christian Heimes <cheimes@redhat.com>
    Reviewed-By: Rob Crittenden <rcritten@redhat.com>
    Reviewed-By: Rob Crittenden <rcritten@redhat.com>