get the trigger list don't support fuzzy matching

[Jie Li]

When we create a cron trigger which is use the create_instance_snapshot workflow. But we cann't query the cron trigger just by instance_id. In other words, the cron trigger list api don't support fuzzy query.

In the mistral code, we find that we limit the "workflow_input" params is jsontype[1], but we only support fuzzy query which the query params type is string[2]. So maybe this is a bug, we should convert it in our mistral code, so that we can query the "workflow_input" fuzzy.

Re:
[1]:https://github.com/openstack/mistral/blob/d0d75be7cbeca4b4445b0799f196feb5ddeb6b1b/mistral/api/controllers/v2/resources.py#L561
[2]:https://github.com/openstack/mistral/blob/d0d75be7cbeca4b4445b0799f196feb5ddeb6b1b/mistral/utils/filter_utils.py#L45