cv: reduce boilerplate with s/gerritfake/gf in tests.
cv: reduce boilerplate with s/gerritfake/gf in tests.

R=qyearsley, yiwzhang

Bug: 1150185
Change-Id: I33b5b12a63c217bd09d045d622cff55bdec1b95d
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-go/+/2552794
Commit-Queue: Andrii Shyshkalov <a30c74fa30536fe7ea81ed6dec202e35e149e1fd@google.com>
Reviewed-by: Quinten Yearsley <747cf52e0cef2e3e9371802a2d344b6c87126a4b@chromium.org>
Reviewed-by: Yiwei Zhang <50b2a565e2e78c292794832469a30ce5abc9959c@google.com>

luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go