fix wrong time offset adjustment

- Always picking the closest bigger time for getting delta can go wrong
  if time changes in the middle.
- If the close bigger time is giving negative time, use the one right
  before it instead.

bug: 33210752
Test: python packages/services/Car/tools/bootanalyze/bootanalyze.py -r -c packages/services/Car/tools/bootanalyze/config.yaml -n 10
Change-Id: Ice44e4839aa9e8d5222e8aa73eb2f7b4329d4757
1 file changed