fix: have a timeout on the wait when closing BigtableIO#Writer

[mutianf]

Batcher#closeAsync already sends out remaining elements and wait on them to finish before closing. Calling closeAsync let us set a timeout on the future and it should not take longer than the operation timeout.

Another hang seems to come from calling service.close() in tearDown. Since we create the service in startBundle, closing the service in finishBundle addresses the issue.

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[Abacn]

Java Tests failures were a hiccup earlier today not related