Improve error output for failing to list npm packages (to help determine why it's failing on build machine)
Add unit test and fix so that we can handle when npm list returns usable output but still returns an error exit code (of 1) when one or more of the modules has missing dependencies

Conflicts:
	tests/com.aptana.js.core.tests/src/com/aptana/js/internal/core/node/NodePackageManagerTest.java