Add @RunWith(JUnit4.class) to all tests

This is not required for Eclipse or Buck, which can figure it out
automatically, but may be for other test environments. For example,
error-prone has a check for missing @Test annotations that only runs
for classes annotated with this runner.

Change-Id: Ib876a5c58b2c8fbb64a1b7d4627bcd0a317bd1f9
18 files changed