client: log items when failed to verify uploaded files
client: log items when failed to verify uploaded files

I'm dougting there is a process who modifies file contents after we
calculate the hash first time in some task failures.
e.g.
https://chromium-swarm.appspot.com/task?id=4bba19b61261d110

Bug: 916644
Change-Id: I7751fd5d923afcea1e5b0bf105c37391e06c79e6
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-py/+/2160589
Reviewed-by: Junji Watanabe <aaef61ef98ffea505db831f310be2a0eb8492537@google.com>
Commit-Queue: Junji Watanabe <aaef61ef98ffea505db831f310be2a0eb8492537@google.com>
Auto-Submit: Takuto Ikuta <71927f930fca81015e0f496c65cd126ab1a692e3@chromium.org>

luci/luci-py,luci/luci-py,luci/luci-py,luci/luci-py