Code to upload a build to crashlytics even when setting a custom apk name.

gradle_fabric_upload.txt

android {
  ...
  debug {
    debuggable true
    ...
    ext.betaDistributionGroupAliases = "Android-Test"
  }
  ...
  project.android.applicationVariants.all { variant ->
    variant.preBuild.doLast {
        variant.outputs.each { output ->
            output.outputFile = new File(output.outputFile.parent, variantApkName(variant, output))
        }
    }
  }
}

android.applicationVariants.all { variant ->
    variant.outputs.each { output ->
        tasks.findAll {
            it.name.startsWith("crashlyticsUploadDistribution${variant.name.capitalize()}")
        }.each {
            it.doFirst {
                ext.betaDistributionApkFilePath = "${buildDir}/outputs/apk/" + variantApkName(variant, output)
            }
        }
    }
}

// Here you choose the custom file naming convention for your apk, also use when actually setting the filename.
def variantApkName(variant, output) {
    return output.outputFile.name.replace(".apk", "-v${variant.versionName}-${variant.versionCode}.apk")
}

// Call ./gradlew crashlyticsUploadDistribution<variant name> to upload to fabric