dashboard: update OpenBSD 6.4 builders to final release

Previously, they were running a 6.4 snapshot release from October 4, 2018,
added in CL 139857.

The final release of OpenBSD 6.4 has been released on October 18, 2018,
and can be used now. See https://www.openbsd.org/64.html.

Fixup unbound variable in env/openbsd-amd64/make.bash:

	$ ./make.bash
	./make.bash: line 57: PKG_ADD_OPTIONS: unbound variable

The amd64 architecture image was tested with cmd/debugnewvm
and passed all tests successfully.

Updates golang/go#26833.

Change-Id: I0e3b1ed5aa9b2e624d9afbe46a8a344f88ddcc56
Reviewed-on: https://go-review.googlesource.com/c/143458
Reviewed-by: Brad Fitzpatrick <[email protected]>

Author: dmitshur

dashboard/builders.go

@@ -147,19 +147,19 @@ var Hosts = map[string]*HostConfig{
 		SSHUsername:        "gopher",
 	},
 	"host-openbsd-amd64-64": &HostConfig{
-		VMImage:            "openbsd-amd64-64-snap1",
+		VMImage:            "openbsd-amd64-64",
 		machineType:        "n1-highcpu-4",
 		buildletURLTmpl:    "https://storage.googleapis.com/$BUCKET/buildlet.openbsd-amd64-64",
 		goBootstrapURLTmpl: "https://storage.googleapis.com/$BUCKET/gobootstrap-openbsd-amd64-64.tar.gz",
-		Notes:              "OpenBSD 6.4 snapshot from Oct 4, 2018; GCE VM is built from script in build/env/openbsd-amd64",
+		Notes:              "OpenBSD 6.4; GCE VM is built from script in build/env/openbsd-amd64",
 		SSHUsername:        "gopher",
 	},
 	"host-openbsd-386-64": &HostConfig{
-		VMImage:            "openbsd-386-64-snap1",
+		VMImage:            "openbsd-386-64",
 		machineType:        "n1-highcpu-4",
 		buildletURLTmpl:    "https://storage.googleapis.com/$BUCKET/buildlet.openbsd-386-64",
 		goBootstrapURLTmpl: "https://storage.googleapis.com/$BUCKET/gobootstrap-openbsd-386-64.tar.gz",
-		Notes:              "OpenBSD 6.4 snapshot from Oct 4, 2018; GCE VM is built from script in build/env/openbsd-386",
+		Notes:              "OpenBSD 6.4; GCE VM is built from script in build/env/openbsd-386",
 		SSHUsername:        "gopher",
 	},
 	"host-freebsd-93-gce": &HostConfig{

env/openbsd-amd64/make.bash

@@ -50,6 +50,7 @@ trap cleanup EXIT INT
 # Currently we download them from the network during the install process.
 
 # Create custom siteXX.tgz set.
+PKG_ADD_OPTIONS=""
 if [[ "$SNAPSHOT" = true ]]; then
   PKG_ADD_OPTIONS="-D snap"
 fi