use npm.common instead of spawn In the process, followed failing code path to command that wasn't respecting the loglevel and updated to RESPECT

Tests that call spawn() and ensure that no stdout/stderr events occur don't seem to work. In particular, the last npm prune test did not catch the stderr event.
This is a case where I think having the options inline is easier to follow, if only because this test code is already so explicit and verbose that it's good to have the relevant options right there. Not saying you should change it back, just explaining why I objected to this change in the first place.