Improve handling of streaming result error situations

Currently if the streaming result times out when waiting to retrieve a row from the queue, a `StopIteration` exception is raised and that exception is not being handled in the `get_next_row` method, but instead it is handled in the `next` method. This could be problematic b/c the handling of `StopIteration` in the `next_` method assumes a normal end to the iteration (i.e. we ended b/c there are no more results) so we then proceed to grab metadata.

NOTE: this impacts all streaming operations (analytics, n1ql, search and view).

This raises a couple of questions:

• How we handle this situation? Retries? Add extra time to the streaming_timeout based on the streaming operation's timeout?
• If this `StopIteration` should terminate streaming, what to we raise to the user?
• Maybe we raise a different error from the streaming result?
• What about the situation where attempting to get metadata fails due to a timeout waiting to retrieve a row from the queue?

With the changes in PYCBC-1521 the SDK now retries in the situation where it receives a `StopIteration` due to a time out when waiting to retrieve a row from the queue. This is essentially the same as using 2x the streaming operation's timeout value. I do not think users should run into this situation (I only see it when I wanted to force , but I would prefer to have as many code paths covered as possible.