WIP: Wait for all pipelines to finish before exiting process

Currently, if you run two pipelines via the CLI, e.g.
`./node_modules/.bin/plumber foo bar`, the CLI will exit as soon as any one of
the pipelines completes. The desired behaviour is that the CLI waits until all
pipelines have completed.

I have attempted to implement this, however my merged observable sequence of
resources never seems to complete. What am I missing?