Leverage local NPM cache to avoid conflicts

The maven build can end up with failure caused by inconsistency of NPM package database such as:

2740 error Failed to parse json
2740 error Unexpected end of input
2741 error File: /home/kpiwko/.npm/minimatch/0.2.14/package/package.json
2742 error Failed to parse package.json data.

In Bower, we use local Bower package database so that it does not conflict with user installation. But NPM still uses global database.