Test with citus triggers

[coco98]

Just had a conversation with Craig today. This landed at citus a few weeks ago:
http://docs.citusdata.com/en/v8.0/extra/triggers.html

At a high-level, Craig said that our updatable views system which uses triggers to enforce ACL can work if the trigger instrumentation is on the coordinator database. When the coordinator rewrites queries for the sharded tables and pushes that out, everything should just work. Triggers running on the sharded database won't work because set local will not be passed down to them.

Let's try things out with citus again and depending on issues we run into we can talk to the engineering folks at Citus to help us out.