Build: use default error handling for PKG_CHECK_MODULES
    
    It turns out that default error handling prints very useful messages
    which are way better than hand-made error handling without any hints.
    
    https://fedorahosted.org/freeipa/ticket/6418
    
    Reviewed-By: Lukas Slebodnik <lslebodn@redhat.com>
    Reviewed-By: Stanislav Laznicka <slaznick@redhat.com>
    Reviewed-By: Christian Heimes <cheimes@redhat.com>