Input validation

[scaleoutsean]

I misread the help file (thought EXISTING_VOLID NAME was EXISTING_VALID_NAME, lol), so it's just a matter of input validation.

# /usr/local/bin/solidfire-docker-driver volume clone --help
NAME:
   solidfire volume clone - create a clone of an existing volume: `clone [options] EXISTING_VOLID NAME`

USAGE:
   solidfire volume clone [arguments...]

# /usr/local/bin/solidfire-docker-driver volume clone sectest
panic: runtime error: index out of range [recovered]
        panic: runtime error: index out of range

goroutine 1 [running]:
panic(0x725da0, 0xc4200120f0)
        /usr/local/go/src/runtime/panic.go:500 +0x1a1
github.com/codegangsta/cli.HandleAction.func1(0xc4200dcb28)
        /root/solidfire-docker-driver-master/src/github.com/codegangsta/cli/app.go:478 +0x247
panic(0x725da0, 0xc4200120f0)
        /usr/local/go/src/runtime/panic.go:458 +0x243
github.com/solidfire/solidfire-docker-driver/sfcli.cmdVolumeClone(0xc420084640)
        /root/solidfire-docker-driver-master/src/github.com/solidfire/solidfire-docker-driver/sfcli/volume.go:204 +0xb8a
reflect.Value.call(0x708580, 0x7ae7a8, 0x13, 0x77efa3, 0x4, 0xc4200dcae8, 0x1, 0x1, 0x5741e8, 0x775580, ...)
        /usr/local/go/src/reflect/value.go:434 +0x5c8
reflect.Value.Call(0x708580, 0x7ae7a8, 0x13, 0xc4200dcae8, 0x1, 0x1, 0x0, 0xc4200dcac8, 0x57cda6)
        /usr/local/go/src/reflect/value.go:302 +0xa4
github.com/codegangsta/cli.HandleAction(0x708580, 0x7ae7a8, 0xc420084640, 0x0, 0x0)
        /root/solidfire-docker-driver-master/src/github.com/codegangsta/cli/app.go:487 +0x1e0
github.com/codegangsta/cli.Command.Run(0x77f4c2, 0x5, 0x0, 0x0, 0x0, 0x0, 0x0, 0x792266, 0x4b, 0x0, ...)
        /root/solidfire-docker-driver-master/src/github.com/codegangsta/cli/command.go:186 +0xc2b
github.com/codegangsta/cli.(*App).RunAsSubcommand(0xc4200c8180, 0xc4200843c0, 0x0, 0x0)
        /root/solidfire-docker-driver-master/src/github.com/codegangsta/cli/app.go:361 +0xa69
github.com/codegangsta/cli.Command.startApp(0x77fa04, 0x6, 0x0, 0x0, 0x0, 0x0, 0x0, 0x786012, 0x17, 0x0, ...)
        /root/solidfire-docker-driver-master/src/github.com/codegangsta/cli/command.go:273 +0x823
github.com/codegangsta/cli.Command.Run(0x77fa04, 0x6, 0x0, 0x0, 0x0, 0x0, 0x0, 0x786012, 0x17, 0x0, ...)
        /root/solidfire-docker-driver-master/src/github.com/codegangsta/cli/command.go:74 +0x1635
github.com/codegangsta/cli.(*App).Run(0xc4200c8000, 0xc42000c1c0, 0x4, 0x4, 0x0, 0x0)
        /root/solidfire-docker-driver-master/src/github.com/codegangsta/cli/app.go:240 +0x611
main.main()
        /root/solidfire-docker-driver-master/src/github.com/solidfire/solidfire-docker-driver/main.go:19 +0x68

I'm using v1.0.0 ;-)