Add support for dockerfile when building

[iffy]

This is my feeble attempt at fixing this. The builds currently fail; I think because of an old version of docker-py. The required docker-py support was added by this: docker/docker-py@0713488 but I can't tell what version that is included in.

This is to fix issue #1228

[iffy]

I didn't sign off the commit, apparently. Well... I'll leave this fix to someone else who is in the groove with this project.

[aanand]

Thanks for the contribution! We're getting close with #1075, but there's some low-hanging fruit in #754 if you feel like adding support for something else.

For future reference, to sign off a commit:

git commit --signoff

To fix a commit that isn't signed off:

git commit --amend --reuse-message=HEAD --signoff

To push your fixed commit if you've already pushed the old one:

git push --force

[iffy]

Oh, it's a known issue being worked on :) That's good. And thanks for the signoff tip -- I'll do that for the next one. Would a programmatic future-proof way of doing #754 be possible? For example:

run-opts: "-foo -bar -whatever=who"

[aanand]

Afraid that wouldn't work, since we don't shell out to docker run - we talk directly to the remote API.

There could be a key for directly setting extra properties on the container JSON, but we'd be opening the door to a lot of misuse.