CB-7670 Fixes failure when trying to fetch dependent plugin while adding platform

Fix for https://issues.apache.org/jira/browse/CB-7670

Problem here is that cordova fetches platform and plugin using NPM and uses different registries for them.
Once npm is initialized using `npm.load()` in lazy_load module, further `npm.load()` (in plugman/fetch.js module) calls ignores provided configuration (https://github.com/npm/npm/blob/master/lib/npm.js#L263)
It seems that the proper way here is to load npm using `npm.load()` and configure it using `npm.config.set()` as described here: https://github.com/npm/npm#using-npm-programmatically