Fix batch / simple processor instrumentation semantics

[jack-berg]

BatchLogRecordProcessor / BatchSpanProcessor / SimpleLogRecordProcessor / SimpleSpanProcessor each call .finish{Signals}(batch.size(), error) after the export has completed.

As @cijothomas notes here, this is wrong. Instead, the processors should call finish immediately after a batch has been submitted to the exporter:

For the SDK Simple and Batching Span Processor a span is considered to be processed already when it has been submitted to the exporter, not when the corresponding export call has finished."

We should fix this.

[ivamly]

I'd like to take this issue. My understanding of the fix: move the .finish{Signals}(batch.size(), error) call to happen immediately after {Signals}exporter.export(...) is invoked, but before result.join(). Please assign this to me.