dashboard: set SkipSnapshot on freebsd-arm and dragonfly-amd64

No point snapshotting for non-sharded builders.

And snapshotting is too slow and hits the timeout on freebsd-arm.

Updates golang/go#21191

Change-Id: I225aa6af493b92aa45589491c69853e13d513dd1
Reviewed-on: https://go-review.googlesource.com/53493
Reviewed-by: Yuval Pavel Zholkover <[email protected]>
Reviewed-by: Brad Fitzpatrick <[email protected]>

Author: bradfitz

dashboard/builders.go

@@ -1211,12 +1211,14 @@ func init() {
 		TryOnly:  true,
 	})
 	addBuilder(BuildConfig{
-		Name:     "dragonfly-amd64",
-		HostType: "host-dragonfly-amd64-tdfbsd",
+		Name:         "dragonfly-amd64",
+		HostType:     "host-dragonfly-amd64-tdfbsd",
+		SkipSnapshot: true,
 	})
 	addBuilder(BuildConfig{
-		Name:     "freebsd-arm",
-		HostType: "host-freebsd-arm-paulzhol",
+		Name:         "freebsd-arm",
+		HostType:     "host-freebsd-arm-paulzhol",
+		SkipSnapshot: true,
 		env: []string{
 			"GOARM=7",
 			"CGO_ENABLED=1",