cmd/coordinator: disable OS X test sharding for now

Workaround until the Mac failures are understood.

Updates golang/go#12979

Change-Id: I15b9ea8f4b708ebf9b7c6ad61e65d0f9eaaa6d73
Reviewed-on: https://go-review.googlesource.com/16440
Reviewed-by: David Crawshaw <crawshaw@golang.org>
diff --git a/dashboard/builders.go b/dashboard/builders.go
index 469d3e2..f14a005 100644
--- a/dashboard/builders.go
+++ b/dashboard/builders.go
@@ -494,7 +494,7 @@
 		Notes:          "Mac Mini running OS X 10.10 (Yosemite)",
 		Go14URL:        "https://storage.googleapis.com/go-builder-data/go1.4-darwin-amd64.tar.gz",
 		IsReverse:      true,
-		NumTestHelpers: 1, // limited resources
+		NumTestHelpers: 0, // disabled per golang.org/issue/12979
 	})
 	addBuilder(BuildConfig{
 		Name:           "darwin-386-10_10",
@@ -502,7 +502,7 @@
 		Go14URL:        "https://storage.googleapis.com/go-builder-data/go1.4-darwin-amd64.tar.gz",
 		IsReverse:      true,
 		env:            []string{"GOARCH=386"},
-		NumTestHelpers: 1, // limited resources
+		NumTestHelpers: 0, // disabled per golang.org/issue/12979
 	})
 	addBuilder(BuildConfig{
 		Name:           "android-arm-sdk19",