cmd/go: vet: provide package ID to the vet tool
cmd/go: vet: provide package ID to the vet tool

This field, which matches the IDs used by go list, will enable all vet
drivers to produce JSON output in a consistent format (a map from
package ID to analysis name to result).

Change-Id: Icac703b944de55df42c996dc2f672005014ad57a
Reviewed-on: https://go-review.googlesource.com/c/149960
Reviewed-by: Russ Cox <5ad239cb8a44f659eaaee0aa1ea5b94947abe557@golang.org>

nawawi/go,nawawi/go,nawawi/go,akutz/go,CAFxX/go,josharian/go,CAFxX/go,CAFxX/go,josharian/go,golang/go,golang/go,nawawi/go,CAFxX/go,cloudflare/go,akutz/go,nawawi/go,akutz/go,CAFxX/go,nawawi/go,cloudflare/go,golang/go,josharian/go,CAFxX/go,cloudflare/go,josharian/go,cloudflare/go,cloudflare/go,golang/go,CAFxX/go,cloudflare/go,akutz/go,josharian/go,cloudflare/go,golang/go,akutz/go,akutz/go,akutz/go,josharian/go,golang/go,nawawi/go,nawawi/go,golang/go,golang/go,cloudflare/go,josharian/go,josharian/go,akutz/go,CAFxX/go