Add sha and tag docker tags

[bcomnes]

In order to facilitate more fine-grained buildbot builds, we need a more fine-grained docker tagging strategy.

This PR does the following:

• Add COMMIT tags to our docker builds
• Adds COMMIT-squash tags to our docker builds
• Add TAG and TAG-squash docker tags when tagged

[sgirones]

The problem I see with using only Jenkinsfile is that there's no way we can test it locally. I would rather have all those steps in a script that you can run and debug.

But just my two cents! And not a big deal

[bcomnes]

@sgirones agreed that the ci flow should be trivially runably locally. It ended up being a bit simpler than this in the end (once I figured out the behavior of the git ENV vars, and a bunch of time out of my day). https://github.com/netlify/build-image/blob/v2.6.7/Jenkinsfile

I think I saw buildbot's cloud builder come with a similar tagging behavior by default, so maybe moving over to that would simplify things even furthur.

If you have a preferred CI pattern for docker image baking, in Jenkins or wherever, I would be happy to consider moving over to it. I'm not attached to this one beyond its what we are running now.

[bcomnes]

@sgirones I'm thinking maybe I didn't understand the original suggestion in the above reply.

Do you mean move all shell scripts into their own file similar to https://github.com/netlify/buildbot/blob/master/script/docker-build.sh ?

Yes! Agreed, if thats the case. I'll clean it up at some point.

[sgirones]

yep! sorry I didn't get back to you.