Add status_path label to connected_clients server metric.

This fixes an issue where the exporter would fail to work if a user
attempted to monitor multiple OpenVPN processes in server mode as the
metrics would clash without the status_path label.

openvpn_exporter.go

@@ -55,7 +55,8 @@ var (
 	// Metrics specific to OpenVPN servers.
 	openvpnConnectedClientsDesc = prometheus.NewDesc(
 		prometheus.BuildFQName("openvpn", "", "openvpn_server_connected_clients"),
-		"Number Of Connected Clients", nil, nil)
+		"Number Of Connected Clients",
+		[]string{"status_path"}, nil)
 
 	openvpnServerHeaders = map[string]OpenvpnServerHeader{
 		"CLIENT_LIST": {
@@ -248,7 +249,8 @@ func CollectServerStatusFromReader(statusPath string, file io.Reader, ch chan<-
 	ch <- prometheus.MustNewConstMetric(
 		openvpnConnectedClientsDesc,
 		prometheus.GaugeValue,
-		float64(numberConnectedClient))
+		float64(numberConnectedClient),
+		statusPath)
 	return scanner.Err()
 }