OVSDriver: do not reinstall kflow with same actions

This requires storing the datapath actions list for each kflow.

This reduces the time to revalidate a kflow whose actions have not
changed by 50%.
OVSDriver: only sync stats during revalidation if OpenFlow flows changed

This reduces the time to revalidate a kflow whose OpenFlow flow set has not
changed by about 90%.
Merge into master from pull request #47:
optimize kflow revalidation (https://github.com/floodlight/ivs/pull/47)