Add download testing

[mhdawson]

After a recent release and issue was opened identifying that the tar.gz was corrupted. There were suggestions in nodejs/node#8814 that we could have an automated job/process that automatically checks the download binaries

[mhdawson]

@gibfahn @richardlau FYI

[jbergstroem]

How about adding a step after creating it instead? something like:

# either
$ gunzip -t $foo.tar.gz && echo $?   # xz supports -t as well
# ..or
$ tar -zxf $foo.tar.gz &> /dev/null && echo $?

[mhdawson]

This looks like a similar issue that we did not notice for smartos as well #585.

Having a regular job that validates we can download/unzip all of the current releases might help.

[gibfahn]

Do we generate md5 checksums for the builds? Seems like something that might be worth doing if we don't.

[gdams]

@mhdawson I'd be happy to quickly script one of these up. I wrote a similar job to automate checking the md5 checksums of the IBM Node releases

[mhdawson]

@gdams that would be great. Once you have the script we can look at setting up the ci to run it.

I can think of a couple of different levels we could valid to:

1. Download and validate unzip works

2. Actually run "hello world", this would mean we'd need to download/unzip on the machine where the version can run.

3. would be great, but 1 would also go a long way to making sure things are ok.

[gdams]

Okay so to start with I have written a simple bash tool that will scrape the download dir for a certain node version and check all of the sha sums. Where abouts would it make sense to store this script?

[gibfahn]

@gdams I'd put it in tools/