dashboard, cmd/coordinator: switch to Windows images with ssh instead of telnet

Fixes golang/go#21150

Change-Id: I568fab0ec8005445ace09e34dd0a8addf73d23d0
Reviewed-on: https://go-review.googlesource.com/51911
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

cmd/coordinator/remote.go

@@ -580,12 +580,17 @@ func handleIncomingSSHPostAuth(s ssh.Session) {
 			"-i", sshPrivateKeyFile,
 			sshUser+"@localhost")
 	case "windows":
+		// TODO(jrjohnson,bradfitz): figure out SSH public key auth on Windows (ACL issues?)
+		// and make this path more like the default case agbove.
 		fmt.Fprintf(s, "# Windows user/pass: gopher/gopher\n")
 		if ipErr != nil {
 			fmt.Fprintf(s, "# Failed to get IP out of %q: %v\n", rb.buildlet.IPPort(), err)
 			return
 		}
-		cmd = exec.Command("telnet", ip)
+		cmd = exec.Command("ssh",
+			"-o", "UserKnownHostsFile=/dev/null",
+			"-o", "StrictHostKeyChecking=no",
+			"gopher@"+ip)
 	case "plan9":
 		fmt.Fprintf(s, "# Plan9 user/pass: glenda/glenda123\n")
 		if ipErr != nil {

dashboard/builders.go

@@ -176,19 +176,19 @@ var Hosts = map[string]*HostConfig{
 		env:         []string{"GO_TEST_TIMEOUT_SCALE=2"},
 	},
 	"host-windows-amd64-2008": &HostConfig{
-		VMImage:            "windows-amd64-server-2008r2-v3",
+		VMImage:            "windows-amd64-server-2008r2-v4",
 		machineType:        "n1-highcpu-4",
 		buildletURLTmpl:    "http://storage.googleapis.com/$BUCKET/buildlet.windows-amd64",
 		goBootstrapURLTmpl: "https://storage.googleapis.com/$BUCKET/go1.4-windows-amd64.tar.gz",
 	},
 	"host-windows-amd64-2012": &HostConfig{
-		VMImage:            "windows-amd64-server-2012r2-v3",
+		VMImage:            "windows-amd64-server-2012r2-v4",
 		machineType:        "n1-highcpu-4",
 		buildletURLTmpl:    "http://storage.googleapis.com/$BUCKET/buildlet.windows-amd64",
 		goBootstrapURLTmpl: "https://storage.googleapis.com/$BUCKET/go1.4-windows-amd64.tar.gz",
 	},
 	"host-windows-amd64-2016": &HostConfig{
-		VMImage:            "windows-amd64-server-2016-v3",
+		VMImage:            "windows-amd64-server-2016-v4",
 		machineType:        "n1-highcpu-4",
 		buildletURLTmpl:    "http://storage.googleapis.com/$BUCKET/buildlet.windows-amd64",
 		goBootstrapURLTmpl: "https://storage.googleapis.com/$BUCKET/go1.4-windows-amd64.tar.gz",