Add debug logs to understand slow update start issue am: e70fa767ae am: c18e35d5a5

Original change: https://android-review.googlesource.com/c/platform/system/update_engine/+/3183139

Change-Id: I32314190b0530653bc42483168c75997e34a6095
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>