Add strong-pm's dependencies' bins to PATH

Replace the fragile fixed path approach with npm-path which does what
npm does in `npm run-script`. This allows any bins provided by our
deps to be found in the $PATH in the environment the app runs in.

SLN-1175 #resolves
Include managed app's dependencies in run PATH

Allow for an application to use a supervisor or runner that is
installed as a dependency of the application without having to install
it on the server or modify the strong-pm environment.