Support labels for containers

[relistan]

This PR adds basic support (without interpolation) for labels at deployment time. These are useful in pretty much all modern Docker deployments.

cc @dselans

[dselans]

What's going to happen when you use labels but deploy to hosts that do not support labels?

[relistan]

Try it, I don't know and I don't have access to a 1.5 Docker daemon to try it. I think Docker will just ignore them.

[relistan]

Want to merge this, but don't want to break things for you @dselans

[relistan]

@actaeon I'd love to merge this but don't want to break things for you guys running Docker 1.5. I don't have 1.5 to test with. Can you or someone else there validate it? Much appreciated.

[actaeon]

@relistan offsite this week :) , will look at it Monday.

[relistan]

Thanks @actaeon !

[relistan]

Ping @actaeon

[relistan]

@intjonathan @actaeon @spkane can one of you guys let me know if this is mergeable? Thanks!

[intjonathan]

Docker 1.5 is very much end of life, we're not running it internally any longer and at this point it seems nobody should. Concerns about compatibility with it have expired too.

[intjonathan]

@relistan Can you weigh in on whether this should be in a 1.9 or 1.8.10?

[relistan]

@intjonathan good, glad no one is running 1.5 :) . Since this is a minor feature addition I'd ship it as 1.8.10. 👍