build: log heap usage

circle.yml

 machine:
   node:
-    version: 6.9.2
+    version: 6.11.4
   python:
     version: 2.7.3
   services:
@@ -30,7 +30,6 @@ dependencies:
     - sudo apt-get update; sudo apt-get install rpm; sudo apt-get install expect
     - ./scripts/build/build_container.sh
 
-
 test:
   override:
     - bash scripts/circle-test.sh

scripts/grunt/options/exec.js

@@ -3,7 +3,7 @@ module.exports = function(config, grunt) {
 
   var coverage = '';
   if (config.coverage) {
-    coverage = '--coverage';
+    coverage = '--coverage --runInBand --logHeapUsage';
   }
 
   return {