iptables: error out on version detection failure

Error out in case the iptables version cannot be determined. It is not
safe assume anything at this point, because execution attempts will most
probably result in errors.

iptables/iptables.go

@@ -18,7 +18,6 @@ import (
 	"bytes"
 	"fmt"
 	"io"
-	"log"
 	"os/exec"
 	"regexp"
 	"strconv"
@@ -55,9 +54,7 @@ func New() (*IPTables, error) {
 	}
 	checkPresent, waitPresent, err := getIptablesCommandSupport()
 	if err != nil {
-		log.Printf("Error checking iptables version, assuming version at least 1.4.20: %v", err)
-		checkPresent = true
-		waitPresent = true
+		return nil, fmt.Errorf("error checking iptables version: %v", err)
 	}
 	ipt := IPTables{
 		path:     path,