Fix broken link in Code Base documentation.
Review Request #8251 — Created June 19, 2016 and submitted
On Running Unit Tests page update hyperlink syntax to correctly reference
nose usage guide.
Built docs and verified that link now goes to the desired page rather than producing a 404.
Tool: Pyflakes Ignored Files: docs/codebase/unit-tests/running-tests.rst Tool: PEP8 Style Checker Ignored Files: docs/codebase/unit-tests/running-tests.rst