Deploygateにgradleからアップロードする際に、メッセージをコンソールから指定する ref: http://qiita.com/shikajiro/items/7a4f26cb4c5fff8b2a93

build.gradle

deploygate {
    userName = "shikajiro"
    token = "hogehoge"

    apks {
        release {
            sourceFile = file("build/outputs/apk/app-release.apk")
            message = deploygateMsg
        }
        debug {
            sourceFile = file("build/outputs/apk/app-debug.apk")
            message = deploygateMsg
        }
    }
}

file2.txt

./gradlew uploadDeployGate -PdeploygateMsg="ここにメッセージ"

gradle.properties

deploygateMsg