Create empty file to fix go build ./...

Go 1.3 broke go build ./... for packages containing test-only
directories. This adds a non-test Go file with no content (besides a
comment explaining its purpose) to the nsqd/test folder, allowing the
repository to once again be built with go build ./...

See issue #409 for more information and issue #381 for links.
I'm on board with that. I just matched the package name in the test file. ;)

How about `donotimport`?