ipa-setup-kra: fix python2 parameter
    
    ipa-setup-kra is failing in python2 with
    invalid 'role_servrole': must be Unicode text
    because of a unicode conversion error.
    
    The method api.Command.server_role_find is called with the parameter
    role_servrole='IPA master' but it should rather be
    role_servrole=u'IPA master'
    
    Fixes: https://pagure.io/freeipa/issue/7897
    Reviewed-By: Christian Heimes <cheimes@redhat.com>