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

[gwarmstrong]

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 #585

[gwarmstrong]

To summarize concisely, we should pick a convention for testing, either all tests in directories named test/ ore tests/, but not a mix of both throughout the project.

[fedarko]

We'll likely need to update a variety of parts of the code that reference these directory names, including .coveragerc, .travis.yml, etc.