dashboard, cmd/coordinator: add concept of trybot-only builders

Make all-compiler a trybot-only builder. This will be used for
temporary sharded ARM trybots.

Updates golang/go#10029

Change-Id: I6cc3188887c2f24edef97d0a9354e39553a15896
Reviewed-on: https://go-review.googlesource.com/10051
Reviewed-by: Andrew Gerrand <[email protected]>

Author: bradfitz

cmd/coordinator/coordinator.go

@@ -569,8 +569,8 @@ func findWork(work chan<- builderRev) error {
 				continue
 			}
 			builder := bs.Builders[i]
-			if _, ok := dashboard.Builders[builder]; !ok {
-				// Not managed by the coordinator.
+			if builderInfo, ok := dashboard.Builders[builder]; !ok || builderInfo.TryOnly {
+				// Not managed by the coordinator, or a trybot-only one.
 				continue
 			}
 			br := builderRev{bs.Builders[i], br.Revision}
@@ -582,8 +582,8 @@ func findWork(work chan<- builderRev) error {
 
 	// And to bootstrap new builders, see if we have any builders
 	// that the dashboard doesn't know about.
-	for b := range dashboard.Builders {
-		if knownToDashboard[b] {
+	for b, builderInfo := range dashboard.Builders {
+		if builderInfo.TryOnly || knownToDashboard[b] {
 			continue
 		}
 		for _, rev := range goRevisions {

dashboard/builders.go

@@ -28,6 +28,7 @@ type BuildConfig struct {
 
 	IsReverse   bool // if true, only use the reverse buildlet pool
 	RegularDisk bool // if true, use spinning disk instead of SSD
+	TryOnly     bool // only used for trybots, and not regular builds
 
 	env []string // extra environment ("key=value") pairs
 }
@@ -184,6 +185,7 @@ func init() {
 	})
 	addBuilder(BuildConfig{
 		Name:        "all-compile",
+		TryOnly:     true, // TODO: for speed, restrict this to builds not covered by other trybots
 		VMImage:     "linux-buildlet-std",
 		machineType: "n1-highcpu-16", // CPU-bound, uses it well.
 		Notes:       "Runs buildall.sh to compile stdlib for all GOOS/GOARCH, but doesn't run any tests.",