Exclude vendor/ from linters

[mcandre]

Could the go vet and gofmt tools please make it easier for users to skip third-party (vendored) code?

For now, I'm wrapping go vet and gofmt with find . -name vendor -prune -o -name '*.go' -exec go vet -v {} \; and find . -name vendor -prune -o -name '*.go' -exec gofmt -s -w {} \;, respectively.

[bradfitz]

Dup of #14417

I'm going to close this because I haven't seen anything to indicate there's been a policy change since that time.