Merge pull request #930 from dalpo/ensure-default-ftp-passive-mode

Ensure the default FTP passive settings to false

The default passive setting has been changed between Ruby 2.2 and 2.3

Sources:
Ruby 2.2: https://docs.ruby-lang.org/en/2.2.0/Net/FTP.html - contains no default_passive, only passive set to false by default
Ruby 2.3: https://docs.ruby-lang.org/en/2.3.0/Net/FTP.html - default_passive set to true by default.

lib/backup/storage/ftp.rb

@@ -50,6 +50,12 @@ def connection
           Net::FTP.send(:remove_const, :FTP_PORT)
         end; Net::FTP.send(:const_set, :FTP_PORT, port)
 
+        # Ensure default passive mode to false.
+        # Note: The default passive setting changed between Ruby 2.2 and 2.3
+        if Net::FTP.respond_to?(:default_passive=)
+          Net::FTP.default_passive = false
+        end
+
         Net::FTP.open(ip, username, password) do |ftp|
           if timeout
             ftp.open_timeout = timeout