updated doc about returning deferred from mocked method
When deleting a group, also delete all the group's events from the events table
Delete group lists policies so that events can be deleted by policy id
updated based on @dried words
Merge pull request #252 from rackerlabs/mock_returns_deferred

updated doc about returning deferred from mocked method
Merge pull request #256 from rackerlabs/auto-419-delete-group-deletes-events

AUTO-419 - delete a group's events from the scaling schedule table
Merge branch 'master' into cron_impl

Conflicts:
	otter/models/cass.py
Using newly committed _delete_events_query_and_params method to delete events in update_delete_events
method and removing delete_events as earlier. Updated tests accordingly