Use the ResourceMap to match test files

Currently, when running tests w/ a file match param, jest is scanning
the filesystem twice: First to match test files, then to build the
resource map. This is quite slow on a large directory structure.

Instead, use the resource map (which contains all file paths) to match
tests.
Can you pull `node-find-files` out of the package.json too? I don't think anything else is using it the source code now