Use always the last TS of the reindex across runs

Keep the last timestamp of the scanning loop and make sure that is
always used across different executions.

The writing of the last timestamp to the underlying file may have delays
whilst it is key to not perform useless reindexing while the file is
getting updated.

Change-Id: I80db1afa43874a82d9b723c6d3456dc7a8f65099
1 file changed