Fix xferquota system test

Fix xferquota system test

The change from RBT to QP has changed the contents of generated zone
files slightly: node names are now always absolute, so instead of using
$ORIGIN and relative names, generated zone files use full names for all
records.

This caused a failure in the xferquota system test, which was looking
for a relative name in secondary zone files. Replace the string
matching with a regular expression to fix the test.

(cherry picked from commit 618c963cb75b3677d5d2e4ff9059a965f09fcb13)