buildenv: temporarily use farmer-ui-test.golang.org as dashboard URL

The build.golang.org service is undergoing a transition as part of
https://golang.org/issue/34744#issuecomment-890076711. It's taking
some time for the DNS change to propagate and HTTPS certificate to
be acquired. During this time, use farmer-ui-test.golang.org as the
dashboard URL, since it's currently used by cmd/coordinator to find
post-submit work and report post-submit build results.

For golang/go#34744.

Change-Id: I7ca99dc75afa2960f831248110c9e5053ee95f99
Reviewed-on: https://go-review.googlesource.com/c/build/+/340589
Trust: Dmitri Shuralyov <[email protected]>
Reviewed-by: Alexander Rakoczy <[email protected]>
Reviewed-by: Carlos Amedee <[email protected]>

Author: dmitshur

buildenv/envs.go

@@ -297,7 +297,7 @@ var Production = &Environment{
 		Name:        "go",
 		MachineType: "n1-standard-4",
 	},
-	DashURL:             "https://build.golang.org/",
+	DashURL:             "https://farmer-ui-test.golang.org/", // TODO(golang.org/issue/47580): Go back to build.golang.org after its DNS rollout stabilizes.
 	PerfDataURL:         "https://perfdata.golang.org",
 	CoordinatorName:     "farmer",
 	BuildletBucket:      "go-builder-data",