[releng] Revert "Remove mirrors"

[Michael Catanzaro <mcatanzaro src gnome org>]

commit 781892db3d303de5c55d06ce232e495ae81dfac3
Author: Michael Catanzaro <mcatanzaro gnome org>
Date:   Mon Feb 17 17:44:59 2020 -0600

    Revert "Remove mirrors"
    
    This reverts commit 8a93a2a0c5c7e95cd17ad1668b2844829ddeb632.
    
    Apparently it doesn't work without this.

 tools/smoketesting/tarball-conversion.config | 4 ++++
 1 file changed, 4 insertions(+)
---
diff --git a/tools/smoketesting/tarball-conversion.config b/tools/smoketesting/tarball-conversion.config
index dad9217..e4ec4eb 100644
--- a/tools/smoketesting/tarball-conversion.config
+++ b/tools/smoketesting/tarball-conversion.config
@@ -51,6 +51,10 @@
     <site module="udisks"                    location="https://udisks.freedesktop.org/releases/"/>
     <site module="uhttpmock"                 location="https://tecnocode.co.uk/downloads/uhttpmock/"/>
   </locations>
+  <mirrors>
+    <mirror location="https://download.gnome.org/"; alternate="file:///ftp/pub/GNOME/" 
host="window.gnome.org" />
+    <mirror location="https://download.gnome.org/"; alternate="sftp://master.gnome.org/ftp/pub/GNOME/"; />
+  </mirrors>
   <!-- Should we remove this functionality? Probably makes more sense to rename modules in BuildStream 
instead. -->
   <rename>
     <name old="gmime3"               new="gmime"/>