fix: log and exit on unhandled promise rejection (#670)

This fixes the issue of pods not restarting on database connection errors. It will also provide
much better visibility into a variety of other unhandled promise rejections we get in Spoke.

Ref: nodejs/node#9523 (comment)

src/server/index.js

@@ -28,7 +28,12 @@ import { r } from "./models";
 import { getRunner } from "./worker";
 
 process.on("uncaughtException", ex => {
-  logger.error("uncaughtException", ex);
+  logger.error("uncaughtException: ", ex);
+  process.exit(1);
+});
+
+process.on("unhandledRejection", err => {
+  logger.error("unhandledRejection: ", err);
   process.exit(1);
 });