add oracle instrumentation

this is instrumentation based on the node-oracle module:
https://github.com/joeferner/node-oracle
we have had similar issues in our mongo instrumentation, I'll have to look into this a bit more, but it might be acceptable to have segments that are not guaranteed to have an end time, the concern would be leaking cursors, so this would only be possible if we can do it such a way that the segment can be gc'd when the client drops their ref to the cursor.