give front-end and back-end test directories the same name

Yeah, we need both. Essentially this file is saying "don't include coverage information for these directories in the total summary"—it was already excluding the `tests/` directory (i.e. `labcontrol/db/tests/`, but it wasn't excluding the `test/` directory for the front-end (`labcontrol/gui/test/`). This change should fix that problem, and the result is that coveralls should now provide a more realistic representation of the code coverage.

...It might also be worth renaming either of the test directories to make them consistent, since having the test directories be named slightly differently is a little bit confusing :)

_Originally posted by @fedarko in https://github.com/biocore/LabControl/pull/585_