Fix a Net::DNS version quirk in the "resolver" system test
Net::DNS versions older than 0.68 insert a ./ANY RR into the QUESTION section if the latter is empty. Since the latest Net::DNS version available with stock RHEL/CentOS 6 packages is 0.65 and we officially support that operating system, bin/tests/system/resolver/ans8/ans.pl should behave consistently for various Net::DNS versions. Ensure that by making handleUDP() return the query ID and flags generated by Net::DNS with 8 zero bytes appended. (cherry picked from commit 6c3c6aea)