Upgrade containerd version and update containerd executor

[svenpopping]

In PR #2568 the "containerd" executor was removed, because it targeted an older version of containerd which was not being maintained anymore.

This PR aims to reintroduce the containerd executor (v1.0.2). This version is being actively maintained.

In the case this PR does not get merged, maybe the following lines, which seem to be related to the previous containerd implementation, should be removed:

[swarmd/main.go:288] mainCmd.Flags().String("containerd-addr", "", "Address of containerd instance of agent.")
[swarmd/main.go:289] mainCmd.Flags().String("containerd-namespace", "swarmd", "Namespace to use when using containerd agent.")

[svenpopping]

The failing test is the same as in issue #2559

[stevvooe]

This is awesome!

My recommendation would be to update to the master branch of containerd. That client will keep us up to date but will work with 1.0+ daemons. There shouldn't too many changes.

[thaJeztah]

ping @ijc @cyli @dperny PTAL

@svenpopping I opened a PR to (temporarily, if this PR gets accepted) remove the unused flags; #2704

If that one gets merged; you can revert the change as part of this PR 👍

[ijc]

I don't have bandwidth for a full review, but FWIW I'm happy to see the code resurrected and maintained. @stevvooe's recommendation to use the containerd master client is a good one, although it might be wise to arrange for CI testing of the different minor versions since you do need to take care which interfaces you use if you want to support older ones in practice.

Somewhat unrelated but IMHO the IDE related .gitignore changes belong locally, either in .git/info/exclude or $HOME/.gitignore not committed to every project.

[thaJeztah]

Somewhat unrelated but IMHO the IDE related .gitignore changes belong locally, either in .git/info/exclude or $HOME/.gitignore not committed to every project.

Ah, yes wanted to point to https://github.com/moby/moby/blob/e5cce50c7ea727c1c901b6e1443bd4291d62fce3/.gitignore#L2-L3 - perhaps we should add a similar line in this repository