scripts/install bootstraps dependencies, but they can't be found afterwards

[NiklasRosenstein]

I think this is because it now installs them into the .nodepy/pip directory of the nodepy-pm package inside the lib/nodepy-modules directory, and no longer into the system- or user-wide Python library directory (as with pip install or pip install --user).

This would be no problem if the nodepy-pm self-installation would be triggered when nodepy-pm was already installed into that directory (it would automatically be able to import it's related Python dependencies), but obviously that's not the case at the time.

To fix it, I think we only need to add to sys.path the install directory of the bootstrapped Pip dependencies.