task copyPackage1(type: Copy) {
    from buildPackage1
    into "/pkgs/"
    eachFile {
        if (it.relativePath.getFile(destinationDir).exists()) {
            throw new GradleException("Probably version was no updated. File exists: " + it)
        }
    }
}
...
task copyPackage2(type: Copy) {
    from buildPackage2
    into "/pkgs/"
    eachFile {
        if (it.relativePath.getFile(destinationDir).exists()) {
            throw new GradleException("Probably version was no updated. File exists: " + it)
        }
    }
}