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

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

Change-Id: I1819db97870a0502072d99d78025c7e84b778b00
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>