zsh: update zsh completion for docker command

zsh completion is updated with the content of
felixr/docker-zsh-completion.

The major change since the last merge is the addition of
exec/create (but they were already present in the docker repository) as
well as pause/unpause/logout/events and the use of short/long options
when they are available. Some missing options were also added.

```
12f00abd7178 Add completion for `exec'
4e2faa075f9a Merge `run' and `create' commands.
34134de077de Add missing long/short options for most commands.
d09f62339ab5 Add completion for `pause' and `unpause'
e4754c3b3b9d Add completion for `logout'
e0935eb3d5d2 Add completion for `events'
dae353cb9afb Add completion for `create`
```

Docker-DCO-1.1-Signed-off-by: Vincent Bernat <vincent@bernat.im> (github: vincentbernat)