Hard-code testing target host

Makefile

@@ -4,7 +4,6 @@ GOOS := plan9
 GOARCH := amd64
 
 test:
-	SDF_PROXY_ALLOWED_HOSTS=teapot-dummy-target.example.com \
 	go test -v
 
 build: test

server_test.go

@@ -7,6 +7,10 @@ import (
 	"testing"
 )
 
+func init() {
+	allowedHosts = []string{"teapot-dummy-target.example.com"}
+}
+
 func TestHttpReverseProxy(t *testing.T) {
 	var header map[string][]string