Remove the relationship between client authentication and the alternative ca cert bundle.

Client authentication isn't the only situation where you might want to override the system ca bundle with an alternative.

ssl_exporter.go

@@ -262,14 +262,7 @@ func main() {
 	kingpin.HelpFlag.Short('h')
 	kingpin.Parse()
 
-	if *clientAuth {
-
-		cert, err := tls.LoadX509KeyPair(*certFile, *keyFile)
-		if err != nil {
-			log.Fatalln(err)
-		}
-		certificates = append(certificates, cert)
-
+	if *caFile != "" {
 		caCert, err := ioutil.ReadFile(*caFile)
 		if err != nil {
 			log.Fatalln(err)
@@ -279,6 +272,14 @@ func main() {
 		rootCAs.AppendCertsFromPEM(caCert)
 	}
 
+	if *clientAuth {
+		cert, err := tls.LoadX509KeyPair(*certFile, *keyFile)
+		if err != nil {
+			log.Fatalln(err)
+		}
+		certificates = append(certificates, cert)
+	}
+
 	tlsConfig = &tls.Config{
 		InsecureSkipVerify: *insecure,
 		Certificates:       certificates,