Add dockerignore

[nikola-rados]

There is a small issue with get_commitish() when we apply a .dockerignore file. Since we remove the .git from the build context there is no git info for the method to pull. I have put a bandaid on it for the moment, but I would like to discuss other options.

Resolves #185.

[rod-glover]

I see what you're doing, and it seems reasonable enough, but maybe unnecessary?

What are your concerns with the gitpython solution? My own would be:

• Leakage of System Resources: "GitPython is not suited for long-running processes (like daemons) as it tends to leak system resources." PDP is definitely long-running.

But a bigger question is:

• The docker-publish action pulls the repo, so there is a .git directory in the larger context. And the original way this was done was that git_commitish was a shell script (so with access to .git, right?) whose value is passed in to the docker build as a build arg. You set something equivalent up in Plan2Adapt. I see that it's a trifle tricky, but obvious enough. Is that not an option here?

Asides:

• You don't specify gitpython as a dependency in setup.py. Was that intentional? Perhaps it would be a bit circular, or at least cart-before-horse there?
• I'm going to assume that the Jenkins fails don't matter.

[rod-glover]

@nikola-rados : Not a big deal, but I have an interest in PDP: What do you make of the alternative (maybe cleaner) method that I noted is used in P2A and elsewehere?

[rod-glover]

@nikola-rados , it looks like this PR was never merged. I think whatever else is done we still need a .dockerignore, but we don't have one in the master branch.

[nikola-rados]

Oh sorry, I lost your comments in my ocean of emails.

I think the alternative is the way to go. I'll restore the branch and see if I can get things working.