Added config options for Jacoco test tasks.

The test tasks used for default Jacoco configuration, including
the report tasks and Sonar execution data.
Only execute JacocoReport if there is any execution data.
Add jacoco as a plugin project.
Fix Jacoco Sonar config when root project doesn't apply Jacoco plugin.

When the Jacoco plugin was applied to a subproject and the Sonar or
Sonar Runner plugin to the root project, the Jacoco reports weren't
configured on the Sonar projects.