Migrate S3 backups from AWS, fix automatic cleanups

The cleanups were broken in that every single archive was also copied to
a shared folder and never deleted from there.

Co-authored-by: Greg Karékinian <greg@karekinian.com>

site-cookbooks/backup/templates/default/config.rb.erb

@@ -23,6 +23,10 @@ Storage::S3.defaults do |s3|
   s3.secret_access_key = "<%= @s3_secret_access_key %>"
   s3.region            = "<%= @s3_region %>"
   s3.bucket            = "<%= node['backup']['s3']['bucket'] %>"
+  s3.fog_options       = {
+    endpoint: "<%= @s3_endpoint %>",
+    aws_signature_version: 2
+  }
 end
 
 Encryptor::OpenSSL.defaults do |encryption|
@@ -88,7 +92,6 @@ end
 
 preconfigure 'KosmosBackup' do
   split_into_chunks_of 250 # megabytes
-  store_with S3
   compress_with Bzip2
   encrypt_with OpenSSL
   notify_by Mail do |mail|