Added confirmation when removing volumes #1437

[grallc]

- What I did
Confirmation is now required for deleting a volume with docker volume rm. (#1437)
It will ask a confirmation for each volumes.

- How I did it
Simply added a condition in /cli/command/volume/remove.go.

- How to verify it
Create some volumes with docker volume create [name] (eg. docker volume create dog-volume, docker volume create cat-volume, docker volume create rabbit-volume) then delete them with docker volume rm (docker volume rm cat-volume dog-volume).

- A picture of a cute animal

[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 "delete-confirmation-1437" git@github.com:grallc/cli.git somewhere
$ cd somewhere
$ git commit --amend -s --no-edit
$ git push -f

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

[thaJeztah]

We can't change the default behavior, because it will likely break many people. I do see the value of having some kind of "interactive" version of docker volume rm, but if we want that, we should think of making this configurable ( in the cli configuration file ~/.docker/config.json).

So in its current form, I don't think we can make this change, but we can discuss options here.