Fix: Pipeline dependency on deb.debian.org, replace with archive

This should fix some tests, as a lot of them are dependent on
deb.debian.org which no longer supports Debian 9 "Stretch".
Instead we use archive.debian.org which will continue to contain
"Stretch" packages for a long time.

system/t04_mirror/ShowMirror5Test_gold

@@ -1,7 +1,7 @@
 {
   "UUID": "82ca6517-ab0b-4be9-81bd-e884a07167f2",
   "Name": "mirror1",
-  "ArchiveRoot": "http://cdn-fastly.deb.debian.org/debian/",
+  "ArchiveRoot": "http://archive.debian.org/debian-archive/debian/",
   "Distribution": "stretch",
   "Components": [
     "main",