Volume labels not persisted across swarm nodes #213

Reproduce

docker volume create --driver convoy --label com.docker.ucp.access.label=KIRBY kirbyVolume

Original volume will have the label, while the duplicated volumes across the swarm nodes will not.

~/D/c/ucptechopsnp ❯❯❯ docker volume inspect kirbyVolume
[
    {
        "Driver": "convoy",
        "Labels": null,
        "Mountpoint": "/",
        "Name": "kirbyVolume",
        "Options": {},
        "Scope": "local"
    }
]

System Info

Docker version

Server:
 Version:      17.03.0-ce
 API version:  1.26 (minimum version 1.12)
 Go version:   go1.7.5
 Git commit:   3a232c8
 Built:        Tue Feb 28 08:10:07 2017
 OS/Arch:      linux/amd64
 Experimental: false

Host

Red Hat Enterprise Linux Server release 7.3 (Maipo)

Convoy

convoy version v0.5.0

Ask

It appears the convoy daemon doesn't support labels, which is probably why docker volumes across the hosts are created without them. We need to be able to restrict access to the volume in Docker UCP using the access label.