Hotkeys only work if value returned from render is a DOM element

[gscshoyru]

Bug report

• Package version(s): Latest
• Browser and OS versions: macOS Sierra

Steps to reproduce

1. Use HotkeysTarget on a class where what's returned from render is a React Component and not a DOM element

Actual behavior

Hotkeys fails to work at all (element is not focus-able, pressing keys don't work)

Expected behavior

Hotkeys work as expected.

Plausibly somewhat related to #931 . The issue is we're cloning the child and adding "onKeyDown" and "tabIndex" props to what we clone -- and if we pass these props to something that's not a DOM element, these props (reasonably) do nothing.