Generate code coverage report from FE unit tests.

I've the following options for getting FE code coverage from test runs:

• Clover (commercial)
• Cobertura (free)
• Jacoco (free)

The tools are all somewhat similar and integrate well with Maven for getting unit and integration test coverage. However, Jacoco seems like a clear winner due to its runtime instrumentation based on a Java agent. This means that it will be easy to also get code coverage for our end-to-end pytests, stress tests and random query tests.

The first task is to use Jacoco for FE unit test coverage.