Test: Use condition_variable to wait for onNat64PrefixEvent am: 4f4f57a8 am:...

Test: Use condition_variable to wait for onNat64PrefixEvent am: 4f4f57a8 am: 735ab8b0 am: 5186aa21

Original change: https://android-review.googlesource.com/c/platform/packages/modules/DnsResolver/+/2825792



Change-Id: I6c35d2d7e5a0542a19ce4e275eae9767b9b67e91
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>