Script fetching Nimbledroid data should return a proper exit code

See this issue for details:
https://github.com/mozilla/firefox-health-dashboard/issues/132#issuecomment-419163074

We also add more verbosity and build the project before calling the script to reflect
code changes to the script.

package.json

@@ -15,7 +15,7 @@
     "start:debugger": "neutrino build && node --inspect .",
     "precommit": "lint-staged",
     "heroku-postbuild": "npm run build",
-    "fetchNimbledroidData": "node build/nimbledroid.js"
+    "fetchNimbledroidData": "neutrino build && node build/nimbledroid.js"
   },
   "lint-staged": {
     "*.js": [

src/scripts/fetchNimbledroidData.js

@@ -35,6 +35,8 @@ const storeProfilingRunIfMissing = async (profilingRunData) => {
     if (!cached) {
       console.log(`Storing ${key}`);
       await redisClient.set(key, JSON.stringify(profilingRunData));
+    } else {
+      console.log(`The key is already in the cache (${key})`);
     }
   }
 };
@@ -48,17 +50,20 @@ const fetchData = async productName =>
   nimbledroidClient.getNimbledroidData(productName);
 
 const main = async () => {
+  let errorCode = -1;
   console.log('Fetching each product can take between 20-40 seconds.');
   try {
     await Promise.all(['klar', 'focus'].map(async (productName) => {
       console.log(`Fetching ${productName}`);
       const productData = await fetchData(productName);
+      console.log(`Storing ${productName}`);
       await storeDataInRedis(productData);
     }));
+    errorCode = 0;
   } catch (e) {
     console.error(e);
   } finally {
-    process.exit();
+    process.exit(errorCode);
   }
 };