Use the IPA API directly when adding the HTTP principal
    
    This is the only way to force in a custom version string
    so that the remote IPA server doesn't reject the request
    as being newer than the server.
    
    This also removes the need to iterate over all servers
    as the IPA connection API does this automatically.
    
    https://fedorahosted.org/ipsilon/ticket/47
    
    Signed-off-by: Rob Crittenden <rcritten@redhat.com>
    Reviewed-by: Nathan Kinder <nkinder@redhat.com>