Jose Fernández

I am fine with the change but I think there should be tests for this. We are already testing the default_shard parameter [here](https://github.com/postgresml/pgcat/blob/3796e26402924f892b06d8b2425c1815e08a1404/tests/ruby/sharding_spec.rb#L110), adding one test case for `fail` should...

I' fine with merging this. What do you think @drdrsh ?