FlowConfig to only run syntactic validation

FlowConfig to only run syntactic validation

- The validate function of FlowConfig class should only run syntactic validation
  The opearational validation like input/output/enqueue port presence, flood
  action on non default container check, etc. should be run only at installation
  time. Also this validation should be run for all the flow installation requests
  either they come from static flow config or from Flow Entry install/modify
  request coming from other bundles.
- With the above change at controller restart, static flow configurations which
  were valid at controller stop but no longer after reboot (for ex. switch sdn
  enabled ports have changed) will still show on the Flow GUI as non installed,
  and their toggling with fail with proper message.

Change-Id: I49d97af49d58102e51a3c8c12db915b60bcb6f4b
Signed-off-by: Alessandro Boch <aboch@cisco.com>