Default to data from 'bulk' rather than 'events' in fetch_open_data
Created by: jkanner
The gwpy 'fetch_open_data' command is great!
The concern was raised in a GWOSC meeting that, if a user asks for time that has both "event" data and "bulk" data, then the command returns "event" data. This might confuse a user who does not know there is an event at that time, and is trying to get a stretch of data from a given run. The suggestion is to have 'fetch_open_data' instead default to bulk data rather than event data.