Since Id4906cbdebd820d3349a4a3211ebb34491516c68, the plugin doesn't need
to check for duplicate security-group rule as the base class will do
this check.
Also explicitly set port-security to default value if not specified in
the request body for create_network, otherwise, some unittest may fail.
Change-Id: I9f44e16616da7a2b79220ce6f37318bb50985470