[bug] go report tells code needs improvement about pouch

[allencloud]

I reassigned this issue to @zhubingbing , and maybe bingbing can help. @Letty5411

[allencloud]

Could you help to solve this for project? @Letty5411

[Letty5411]

@allencloud OK

[zhubingbing]

1. Issue Description

go vet examines Go source code and reports suspicious constructs, such as Printf calls whose arguments do not align with the format string.
pouch/cli/pull.go
Line 94: error: unrecognized printf verb 'r' (vet)
Line 102: error: unrecognized printf verb 'r' (vet)
Line 109: error: unrecognized printf verb 'r' (vet)

i think fmt.Sprintf formate don’t have “r” parameter, so go vet report this issue.
if an operand implements the Formatter interface, it will be invoked. Formatter provides fine control of formatting.（https://golang.org/pkg/fmt/#Fprintf）
and bar.go(https://github.com/containerd/containerd/blob/master/progress/bar.go#L21) to realize formatter interface. so i thinks there's no problems with this code .

[allencloud]

Actually with my own go vet on my local machine, it will report no error:

pouch (master) $ go vet cli/pull.go
pouch (master) $ go version
go version go1.8.3 darwin/amd64
pouch (master) $

So maybe we can ignore this, and please move on on your work. @zhubingbing
Thanks a lot.