Test: Some comments and small fixes for PrivateDnsDohTest am: cdb5bbc9 am: 6f952575 am: 4dd8096c am: 3fe29451

Original change: https://android-review.googlesource.com/c/platform/packages/modules/DnsResolver/+/2447582



Change-Id: I6c0be21f04006293c398a12b073705535521fba9
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>