nebraska: Add timestamp to logs

This will help with debugging when comparing logs with update_engine.

BUG=b:187098215
TEST=./nebraska.py --runtime-root /tmp # The log looks like:
2021-06-03 09:48:33,785 INFO     Starting nebraska ...
2021-06-03 09:48:33,785 DEBUG    Config updated to:

Change-Id: I30dde517119467cfef85e5e8017f2de841d8e838
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/dev-util/+/2937217
Tested-by: Amin Hassani <ahassani@chromium.org>
Commit-Queue: Amin Hassani <ahassani@chromium.org>
Reviewed-by: Jae Hoon Kim <kimjae@chromium.org>
1 file changed