app level build.gradle file to create Gradle's custom task "inernalQADist" that Jenkins calls to build and distribute the apk and also send the notification to a Slack Channel for Internal QA Team

build.gradle

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