Merge Jacoco coverage reports for multiproject setups

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The JacocoMerge is probably more correct, but a common alternative is the jacocoRootReport style task. The example below is how you can create an aggregate report and publish to Coveralls. You can dig into the usage here if you run into problems.

task jacocoRootReport(type: JacocoReport, group: 'Coverage reports') {
  description = 'Generates an aggregate report from all subprojects'
  dependsOn(subprojects.test)

  additionalSourceDirs = files(subprojects.sourceSets.main.allSource.srcDirs)
  sourceDirectories = files(subprojects.sourceSets.main.allSource.srcDirs)
  classDirectories = files(subprojects.sourceSets.main.output)
  executionData = files(subprojects.jacocoTestReport.executionData)

  reports {
    html.enabled = true
    xml.enabled = true
  }

  doFirst {
    executionData = files(executionData.findAll { it.exists() })
  }
}

coveralls {
  sourceDirs = subprojects.sourceSets.main.allSource.srcDirs.flatten()
  jacocoReportPath = "${buildDir}/reports/jacoco/jacocoRootReport/jacocoRootReport.xml"
}