Merge pull request #835 from mrjana/overlay

Don't treat non-nil output as error in ChainExists

libnetwork/drivers/overlay/filter.go

@@ -23,7 +23,7 @@ func rawIPTables(args ...string) error {
 }
 
 func chainExists(cname string) bool {
-	if err := rawIPTables("-L", cname); err != nil {
+	if _, err := iptables.Raw("-L", cname); err != nil {
 		return false
 	}