Pass ipa-ca-agent credentials as PEM files
    
    In Fedora 27 curl is proposing to switch to using OpenSSL as
    the crypto backend instead of NSS. This requires a new set of
    arguments to certmonger to bootstrap fetching the IPA RA cert.
    
    https://pagure.io/freeipa/issue/7076
    
    Reviewed-By: Stanislav Laznicka <slaznick@redhat.com>