<nodejs cartridge> Fix npm link for SCL versions

npm link was being run in the system context instead of the SCL context
during install if an SCL version is chosen.

only attempt to link modules that are both in the npm_global_module_list
and installed on the system

nodejs_context uses $OPENSHIFT_NODEJS_VERSION, but since this variable
is also set in the bin/install script, need to explicitly set the
variable to prevent errors with using nodejs_context in bin/install