Re-add "Region" to uploadCmdData struct

https://github.com/mitchellh/packer/commit/af89b31a4067e2acd1f9c5f370a90218885a29be removed "Region" which prevents the --region parameter being used (dynamically) in "bundle_upload_command".  For example, currently:
``
"bundle_upload_command": "sudo -in ec2-upload-bundle -b {{.BucketName}} -m {{.ManifestPath}} -a {{.AccessKey}} -s {{.SecretKey}} -d {{.BundleDirectory}} --batch --region {{.Region}} --retry"
``
causes:
``
Build 'amazon-instance' errored: Error processing bundle upload command: template: tpl29:1:146: executing "tpl29" at <.Region>: Region is not a field of struct type instance.uploadCmdData
``