Test: Add more helper functions for private DNS validation events am: 7656f200

Original change: https://android-review.googlesource.com/c/platform/packages/modules/DnsResolver/+/2685926



Change-Id: I9b6c1b32564a92e8d35f04b87b089aa9415a5aad
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>