[CB-3798] Provide support for optional localized node/npm/bb-tools

-Several script updates to provide support for optional localized binaries [node/npm/bbtools]
-Added support for overridable global CORDOVA_NODE env variable to point to node installation
-Added support for overridable global CORDOVA_BBTOOLS env variable to point to bbndk tools
-Run plugman via JS and not command-line