Add test coverage for WriteAheadStorage.

Reviewed at https://reviews.apache.org/r/27542/
Create the PyCharm project configuration for easier IDE setup.

Reviewed at https://reviews.apache.org/r/27779/
Fix false passing test case in SchedulerDriverServiceTest.

Reviewed at https://reviews.apache.org/r/27772/
Make it easier to request another ReviewBot run, and flag diffs that seem to lack test coverage.

Reviewed at https://reviews.apache.org/r/27770/