cv: show cancellation reason in CV status app
cv: show cancellation reason in CV status app

R=tandrii

Bug: 1215612
Change-Id: I539bf566d8df79a880c6ea8fe9451f5148882cfd
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-go/+/3217867
Commit-Queue: Yiwei Zhang <50b2a565e2e78c292794832469a30ce5abc9959c@google.com>
Reviewed-by: Andrii Shyshkalov <a30c74fa30536fe7ea81ed6dec202e35e149e1fd@google.com>

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