bootanalyze: do timeout when there is no logcat input

- timeout (-w option) did not work when a new log is not
  available and the script can be stuck forever.
- use poll to timeout on read

bug: 36526636
Test: python packages/services/Car/tools/bootanalyze/bootanalyze.py -r -c packages/services/Car/tools/bootanalyze/config.yaml -n 100 -f -e 15 -w 50
Change-Id: I95208651582a43be5f4692a8499ad78b9c204256
1 file changed