fix(Resolve): prevent RXWAIT from waiting for the observable to complete

[adharris]

The RXWAIT resolve policy is supposed to wait for the resolved observable to begin emitting values, and then provide the observable. It accomplishes this by first cache()ing the observable and then waiting on the result of toPromise. However, RxJS toPromise only resolves the promise when the stream completes, not when the first value is emitted as desired. Adding take(1) before toPromise will cause the stream to complete after 1 value is emitted, at what point the original stream can be returned.

Also, the cache() without a buffer size will cause all old results to be replayed to new subscribers. Setting a buffer size of 1 will cause only the most recent emitted value to be replayed.