OfflineContentGenerator: Use new -npm jobs

Apparently the -npmtest macro is being deprecated (and I was running
into test problems with it anyways needing to keep the explict
node_modules repo up to date.)

Also: I9020ea6e1aa16ce61b32efa708f94d3a3c341585

Change-Id: Ia82779635d762a31bc90ab5c6a44efac1acc2b5a