Fix db connection count tracking

The previous version with events literally only fired on startup of
instances and then never again, making it not useful for showing neat
graphs.

This fixes it by sending the current count every 5s, no matter if it
changes or not, which is how DataDog expects it to be.

Author: Max Stoiber

shared/db/db.js

@@ -59,9 +59,9 @@ poolMaster.on('queueing', size => {
   statsd.gauge('db.query_queue.size', size);
 });
 
-poolMaster.on('size', size => {
-  statsd.gauge('db.connections.count', size);
-});
+setInterval(() => {
+  statsd.gauge('db.connections.count', poolMaster.getLength());
+}, 5000);
 
 // Exit the process on unhealthy db in test env
 if (process.env.TEST_DB) {