Patch to fix libnetwork cutting off streaming connections on update

[YarekTyshchenko]

This seems to be related to PR moby/moby#30321, which actually has two
underlying issues:

1. After starting new container, the old container, being in shutdown phase, still receives new connections.
2. After issuing container shutdown, existing connections are cut, instead
   of waiting for the container to cut them off as part of its shutdown.

Problem 1 seems to be fixed in 18.02, but problem 2 remains.

This patch seems to honour the stop_grace_period defined in the compose file.

Disclaimer:
I seem to have assembled this patch from two other patches that I found in the above PR thread. One is:
hjdr4/libnetwork@234cdaa
and another one that I can't find (one that gets the endpoint from the store). However, testing it
with https://github.com/YarekTyshchenko/docker-rolling-upgrade-test/tree/streams seems to work fine.

[GordonTheTurtle]

Please sign your commits following these rules:
https://github.com/moby/moby/blob/master/CONTRIBUTING.md#sign-your-work
The easiest way to do this is to amend the last commit:

$ git clone -b "18.02-small-patch" [email protected]:awin/docker-ce.git somewhere
$ cd somewhere
$ git rebase -i HEAD~842354015536
editor opens
change each 'pick' to 'edit'
save the file and quit
$ git commit --amend -s --no-edit
$ git rebase --continue # and repeat the amend for each commit
$ git push -f

Amending updates the existing PR. You DO NOT need to open a new one.

[thaJeztah]

Thanks for contributing, however, the files that are updated in this PR are vendored files, and should be changed upstream (in docker/libnetwork), and re-vendored in upstream Moby/moby first.

Based on priority/urgency, fixes can be backported from moby/moby after that.

I'll close this PR, but feel free to continue the conversation

[YarekTyshchenko]

Yes, @thaJeztah, happy for this to be closed. As @abhi pointed out that the issue is confirmed, but you have chosen to go down a different path, in the corresponding commit in libnetwork: moby/libnetwork#2074 (comment)

I look forward to seeing what you all come up with! ❤️