Fix missing coincidence FAR calculation

In the raven.coincidence_search we call the raven.search function and pass the result in parallel to raven.add_exttrig_to_superevent and raven.call_coinc_far

This should fix the missing superevent_id from the superevent dictionaries from the raven coincidence search when we run on an external trigger.

Also, all the test scenarios for test_raven_coincidence_search have been restored