Default bridge need not have persistence in bridge driver

Signed-off-by: Madhu Venugopal <madhu@docker.com>

drivers/bridge/bridge_store.go

@@ -193,7 +193,7 @@ func (ncfg *networkConfiguration) Exists() bool {
 }
 
 func (ncfg *networkConfiguration) Skip() bool {
-	return false
+	return ncfg.DefaultBridge
 }
 
 func (ncfg *networkConfiguration) New() datastore.KVObject {

network.go

@@ -623,7 +623,10 @@ func (n *network) deleteNetwork() error {
 		if _, ok := err.(types.ForbiddenError); ok {
 			return err
 		}
-		log.Warnf("driver error deleting network %s : %v", n.name, err)
+
+		if _, ok := err.(types.MaskableError); !ok {
+			log.Warnf("driver error deleting network %s : %v", n.name, err)
+		}
 	}
 
 	return nil