enable tests custom directories

Summary: Hard-coded directory made it impossible to run the tests.

Test Plan:

1. build the project
2. run make test

Expected results: tests run
Actual result without patch: some error message
Actual result with patch applied: tests run, 2 failing - unrelated, though

Reviewers: #guam_developers

Projects: Guam

Differential Revision: https://git.kolab.org/D98