Tweak ordering of snapshot URLs

Put snapshot.d.o last in the list in jigdo files, to reduce load on
the service.

Backported from current HEAD

debian/changelog

@@ -17,6 +17,8 @@ debian-cd (3.1.21-stretch) UNRELEASED; urgency=medium
       - Generate checksums for torrents and jigdo files too if desired
       - Tweak the code ordering in update-cd so the jigdo file checksums
         are generated after they're compressed.
+      - Tweak ordering of snapshot URLs - put snapshot.d.o last in the list in
+        jigdo files, to reduce load on the service.
 
  -- Steve McIntyre <93sam@debian.org>  Mon, 19 Jun 2017 13:39:58 +0100
 

tools/jigdo_cleanup

@@ -40,22 +40,22 @@ cat $jigdo | awk -v ISO="$iso" -v TEMPLATE="$template" -v DISCINFO="$discinfo" -
 ' > $jigdo.1
 mv -f $jigdo.1 $jigdo
 
-# Snapshot URL
-if [ "$snapurl"x != ""x ] ; then
-    echo "$snapurl" >> $jigdo
-fi
-
 # If some fallbacks were specified, output a servers section with the
 # URLs. The entries of the variable are expected to be already of the
 # form "Label=http://some.url/"
 if test -n "$JIGDOFALLBACKURLS"; then
     for url in "$JIGDOFALLBACKURLS"
     do
+        echo "$url" >> $jigdo
+    done
+fi
+
+# Snapshot URL - use last
+if [ "$snapurl"x != ""x ] ; then
     # The --try-last switch assigns a lower priority to the URL,
     # so it will only be used if other server entries (without the
     # --try-last) have already been tried without success.
-        echo "$url --try-last" >> $jigdo
+    echo "$snapurl --try-last" >> $jigdo
-    done
 fi
 
 # Create a snapshot tree if we've been told where to create one