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/149960Reviewed-by: Russ Cox <rsc@golang.org>