File uploads - Nesting integration test

[BrynCooke]

The original file upload spec supports having the uploaded file be nested in either an object or a list. The current tests only test for root-level variables. An example of the kind of request we would want to test is as follows:

mutation Upload {
  uploadList($files: [Upload!]! { ... }
  uploadObject($nestedFile: NestedFile) { ... }
}

type NestedFile {
  file: Upload
}