dashboard: upsize windows-amd64-{longtest,race} builders to 14.4 GB RAM

Start using n1-highcpu-16 machine type instead of n1-highcpu-8
for windows-amd64-longtest and windows-amd64-race builders.

The primary motivation of this change is to increase amount of
RAM available on the race builder from 7.2 GB to 14.4 GB.
CL 208500 has helped by going from 3.6 to 7.2, but empirically
8 GB is not enough for all tests to pass, while 16 GB can be.
We already use 16 GB for some other race and/or long builders.

Updates golang/go#35186
Updates golang/go#33951
Updates golang/go#33986

Change-Id: I8031a517e6e44ce5e5faba085e7c781a1fcab92e
Reviewed-on: https://go-review.googlesource.com/c/build/+/213557
Reviewed-by: Brad Fitzpatrick <[email protected]>

Author: dmitshur

dashboard/builders.go

@@ -436,9 +436,9 @@ var Hosts = map[string]*HostConfig{
 		SSHUsername:        "gopher",
 	},
 	"host-windows-amd64-2008-big": &HostConfig{
-		Notes:              "Same as host-windows-amd64-2008, but on n1-highcpu-8",
+		Notes:              "Same as host-windows-amd64-2008, but on n1-highcpu-16",
 		VMImage:            "windows-amd64-server-2008r2-v7",
-		machineType:        "n1-highcpu-8", // 8 vCPUs, 7.2 GB mem
+		machineType:        "n1-highcpu-16", // 16 vCPUs, 14.4 GB mem
 		buildletURLTmpl:    "http://storage.googleapis.com/$BUCKET/buildlet.windows-amd64",
 		goBootstrapURLTmpl: "https://storage.googleapis.com/$BUCKET/go1.4-windows-amd64.tar.gz",
 		SSHUsername:        "gopher",
@@ -458,9 +458,9 @@ var Hosts = map[string]*HostConfig{
 		SSHUsername:        "gopher",
 	},
 	"host-windows-amd64-2016-big": &HostConfig{
-		Notes:              "Same as host-windows-amd64-2016, but on n1-highcpu-8",
+		Notes:              "Same as host-windows-amd64-2016, but on n1-highcpu-16",
 		VMImage:            "windows-amd64-server-2016-v7",
-		machineType:        "n1-highcpu-8", // 8 vCPUs, 7.2 GB mem
+		machineType:        "n1-highcpu-16", // 16 vCPUs, 14.4 GB mem
 		buildletURLTmpl:    "http://storage.googleapis.com/$BUCKET/buildlet.windows-amd64",
 		goBootstrapURLTmpl: "https://storage.googleapis.com/$BUCKET/go1.4-windows-amd64.tar.gz",
 		SSHUsername:        "gopher",