Don't write normal operational message to stderr

This prevents sending out unnecessary mails when run from the related
cron job:

   condense-mirrorlogs.cron
-> condense-mirrorlogs.sh > /dev/null
-> mirrorlist.py

Additionally, report the failing file name in the case of an error.

Signed-off-by: Nils Philippsen <nils@redhat.com>

roles/web-data-analysis/files/mirrorlist.py

@@ -586,12 +586,12 @@ def parselog(our_file, out_file):
 
     our_list = list(yumclients_set)
     our_list.sort()
-    
+
     try:
         output = open(output_file,"a")
-        sys.stderr.write("Outputting data: %s\n" % our_file)
+        sys.stdout.write("Outputting data: %s\n" % our_file)
     except:
-        sys.stderr.write("Unable to open outputfile\n")
+        sys.stderr.write("Unable to open outputfile: %s\n" % our_file)
         sys.exit(-1)
 
     for line in our_list: