Fix assertRaisesMessage calls on Python 2.7.9/2.7.10.
Review Request #7453 — Created June 25, 2015 and submitted
assertRaisesMessage on Python 2.7.9/2.7.10 has a known bug where it can't be used as a context manager. This fixes the code to use the old-style invocation, where a lambda is passed in, allowing the tests to run again.
Unit tests now pass.
Tool: Pyflakes Processed Files: reviewboard/hostingsvcs/tests.py Tool: PEP8 Style Checker Processed Files: reviewboard/hostingsvcs/tests.py