custom Gradle task "externalQADist" that Jenkins calls to build and distribute the apk and also send the notification to a Slack Channel for External QA Team

build.gradle

// Used by Jenkins to distribute apk among External Testers via Fabric Beta
task externalQADist (type: GradleBuild) {
    group 'MyApp Distribution'
    description 'Task for Jenkins to distribute Build for External QA'
    tasks = ['clean',
             'cleanBuildCache',
             'assembleExternalQA',
             'crashlyticsUploadDistributionExternalQA']
}