<config>
    <agent>
      ...
      <flow-cache>
         <timeout>300</timeout> <!-- seconds -->
      </flow-cache>
      ...
    </agent>
</config

timeout option is not present - Agent behaves existing way.
timeout is present - No traffic for configured timeout, flows will be deleted.
timeout is present, but 'timeout' value as '0' - Agent behaves existing way.
Merge github.com:Juniper/contrail-controller into HEAD
Merge pull request #415 from Juniper/flow_cache_timeout

Flow cache timeout