Support sourcing the IPA server name from config
    
    Use ding-libs to parse /etc/ipa/default.conf to find the IPA server
    to contact by default.
    
    Signed-off-by: Simo Sorce <simo@redhat.com>
    
    Ticket: https://fedorahosted.org/freeipa/ticket/2203
    Reviewed-By: Fraser Tweedale <ftweedal@redhat.com>