dillon1000/react

Fix MultiChild tests so they work with Fiber

Dropped the unnecessary use of findDOMNode.
Dropped unnecessary arrow functions.
Math.random() -> id counter, since this used to be
non-deterministic which is not ideal for unit tests.

getOriginalKeys() used to rely on implementation details
to scan that the internal data structure maintained its
structure, however, since that is unobservable we don't
need to test the internal data structure itself. We're
already testing refs and dom structure which is the only
observable effect of the reorder.