Revert "Revert graylog output"

This reverts commit 4f27315720.

plugins/outputs/graylog/README.md

@@ -3,3 +3,12 @@
 This plugin writes to a Graylog instance using the "gelf" format.
 
 It requires a `servers` name.
+
+### Configuration:
+
+```toml
+# Send telegraf metrics to graylog(s)
+[[outputs.graylog]]
+  ## Udp endpoint for your graylog instance.
+  servers = ["127.0.0.1:12201", "192.168.1.1:12201"]
+```

plugins/outputs/graylog/graylog_test.go

@@ -24,7 +24,6 @@ func TestWrite(t *testing.T) {
 	i.Connect()
 
 	metrics := testutil.MockMetrics()
-	metrics = append(metrics, testutil.TestMetric(int64(1234567890)))
 
 	i.Write(metrics)