Allow to use installable-item.js as module in requirements.json
Allow to use installable-item.js as module in requirements.json

This fix lets to use installable-item.js as module for installers declared
in requirements.json. It would just download declared item in cache and
installation just calls success method.

dgolovin/developer-platform-install,dgolovin/developer-platform-install,redhat-developer-tooling/developer-platform-install,redhat-developer-tooling/developer-platform-install