Make Jacoco work with multiple test tasks (#437)

* Make Jacoco work with multiple test tasks

By default Jacoco only looks at execution data from
the 'test' task. This is a problem to 'core' which
has multiple test sets.

java_common.gradle

@@ -121,6 +121,11 @@ spotless {
   }
 }
 
+jacocoTestReport {
+    // Use coverage data from all tests tasks, not just the one named 'test'.
+    getExecutionData().setFrom(fileTree(buildDir).include("/jacoco/*.exec"))
+}
+
 // Initialize for coverage minimum determination for each sub project.
 task initCoverageMinimums {
   // Use current coverage ratio of each subproject as placeholder value.