m/test/e2e: stop downloading container images

Having tests rely on The Internet isn't great, having tests rely on the
Dockercorp registry is even worse. Instead, let's test everything using
the preseed_test image.

Change-Id: Ib82ce266592e9c6d2f0d4597abcc114c12746b1f
Reviewed-on: https://review.monogon.dev/c/monogon/+/1338
Tested-by: Jenkins CI
Reviewed-by: Lorenz Brun <lorenz@monogon.tech>
diff --git a/metropolis/test/e2e/preseedtest/main.go b/metropolis/test/e2e/preseedtest/main.go
index ceb3898..a44377f 100644
--- a/metropolis/test/e2e/preseedtest/main.go
+++ b/metropolis/test/e2e/preseedtest/main.go
@@ -16,8 +16,18 @@
 
 package main
 
-import "fmt"
+import (
+	"fmt"
+	"net/http"
+)
 
 func main() {
 	fmt.Println("Hello world from preseeded image")
+	http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
+		fmt.Fprintf(w, "Hello world from preseeded image\n")
+	})
+	err := http.ListenAndServe(":80", nil)
+	if err != nil {
+		fmt.Printf("Serve failed: %v\n", err)
+	}
 }