Enhancing Flow Audit to do faster cleanup of Hold Entries.
loop through 1K entries every 500 ms so that scan of flow table
is finished in 4 mins 16 secs, compared to 17 mins.
Addressing Review comment to avoid using UTCtimestamp.
instead use the timer value to increment the timestamp every timer run.

- spelling correction for yield.
Merge pull request #71 from Prabhjot-Sethi/master

Enhancing Flow Audit to do faster cleanup of Hold Entries.