On pywikibot/i18n repository, the npm job works just fine but the Nodepool based version npm-node-4.3 breaks with:
Running "banana:all" (banana) task Warning: Unable to read "/home/jenkins/workspace/npm-node-4.3/log/qqq.json" file (Error code: ENOENT). Use --force to continue.
The reason is npm-node-4.3 clone the repository under $WORKSPACE and then we create a directory $WORKSPACE/log which ends up polluting the source checkout.
The CI job must not pollute the source checkout!