Fix and modernize currentop.js

The test doesn't properly wait for the operations to be running when using the mmapv1 storage engine. It looks for operations to report holding or waiting for the "w" or "r" collection locks, which represent intent locks. This won't happen on mmapv1. Instead, the operations will report holding or waiting for the "W" or "R" collection locks respectively (the non-intent versions of these locks, which are not compatible with each other).

While fixing the test, we should clean up the numerous unnecessary print statements, single letter variable names, etc. which make the test difficult to read and diagnose.