Add information for Manager Addresses in the output of docker info

[yongtang]

- What I did
As is specified in #28018, it would be useful to know the manager's addresses even in a worker node. This is especially useful when there are many worker nodes in a big cluster.

The information is available in info.Swarm.RemoteManagers.

This fix add the information of Manager Addresses to the output of docker info, to explicitly show it.

- How I did it

- How to verify it

A test has been added for this fix.

Also the new output:

$ docker info
...
Cgroup Driver: cgroupfs
Plugins: 
 Volume: local
 Network: bridge host macvlan null overlay
Swarm: active
 NodeID: bu6m8b45fxu8ac4w4wx26iw19
 Is Manager: false
 Node Address: 127.0.0.1
 Manager Addresses: 127.0.0.1:2477
Runtimes: runc
Default Runtime: runc
...

- Description for the changelog

- A picture of a cute animal (not mandatory but encouraged)

This fix fixes #28018.

Signed-off-by: Yong Tang yong.tang.github@outlook.com

[allencloud]

I was wondering if there is lots of managers, this line could be some kind of unreadable. Is it OK for separate line for each one? Just my thoughts.

[yongtang]

Thanks @allencloud. The PR has been updated with separated lines.

[allencloud]

Or just show the address of leader manager?

[yongtang]

@allencloud To show the lead manager is slightly tricky because it needs to query other managers to get the leader. If there is an error while querying managers, not sure we should return an error (error for docker info), or we should just ignore.

[vdemeester]

/cc @aluzzardi @stevvooe @aaronlehmann

[stevvooe]

Or just show the address of leader manager?

Also, the utility of knowing the leader is limited, since it may change at any time. From the perspective of a client, the managers should be treated equally. The current leader should only be of interest the quorum.

[allencloud]

Thanks @stevvooe
I think we need to think more about whether to bring this or how to bring this better.
If we have lots of managers, docker info would be not so reasonable than before with a list of manager address. I got your point of leader's meaningless for client.

In addition, a rebase needed, though. @yongtang

[yongtang]

Thanks @allencloud, rebased.

[thaJeztah]

Sorry @yongtang rebase needed again 😢 (it's busy before code freeze 😄)

[yongtang]

Thanks @thaJeztah. The PR has been rebased. 😅

[aaronlehmann]

LGTM

[tonistiigi]

@yongtang needs rebase

LGTM

[yongtang]

Thanks @tonistiigi @aaronlehmann for the review. The PR has been rebased.

[thaJeztah]

I added this to the 1.13 milestone, @yongtang can you do a follow up PR for docs?

[yongtang]

Thanks @thaJeztah . Since this PR only changes the output of docker info and there is no API changes, I only updated the docs/man for docker info in PR #28316.

[thaJeztah]

Perfect, thanks! i'll review later