gerrit: Add additional fields to RevisionInfo
gerrit: Add additional fields to RevisionInfo

This adds revision creation date, git ref, and fetch info to the Gerrit
RevisionInfo type.  In particular, adding fetch info allows the caller
to include "DOWNLOAD_COMMANDS" as a field to return in queries; this can
be useful in automation.

Change-Id: I407024b2d50278f7179bc589cbe29fa279d5ab78
Reviewed-on: https://go-review.googlesource.com/13896
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

evandbrown/build,proppy/build,golang/build,proppy/build,golang/build,proppy/build,evandbrown/build,golang/build,evandbrown/build,proppy/build,golang/build