"smartsign" system test: properly detect presence of CDS/CDNSKEY records

Replace grep calls with awk scripts to more precisely detect presence of CDS and CDNSKEY records in a signed zone file, in order to prevent rare false positives for the "smartsign" system test triggered by the strings "CDS" and/or "CDNSKEY" being accidentally present in the Base64 form of DNSSEC-related data in the zone file being checked.