Ignore vendored packages when `go vet`
Ignore vendored packages when `go vet`

[#158403242](https://www.pivotaltracker.com/story/show/158403242)

Co-authored-by: Andrew Gilbert <b4118a773447c7e1e7a545f299a655d91bf11297@pivotal.io>

mattcui/bosh-agent,gu-bin/bosh-agent,gu-bin/bosh-agent,gu-bin/bosh-agent,cloudfoundry/bosh-agent,mattcui/bosh-agent,mattcui/bosh-agent,cloudfoundry/bosh-agent