Use $target_file in *_get variables, not $name

When a user specifies the `$target` parameter in a `staging::file` defined type, the intention is to fetch the file from `$source` and place it at `$target`. When `$name` is used in the `$http_get` variants, the retrieved file won't actually be placed at the `$target` location. This commit makes it so that curl and wget will always place the retrieved file in the `$target_file` location. This should not impact the behavior when a user doesn't specify `$target`, but should fix the unexpected behavior when they do.