Make bloom WAL test compare psql output text, not just result codes;
this was evidently the intent all along, but it was mis-coded.
In passing, make sure we will notice any failure in setup steps.

Alexander Korotkov, reviewed by Michael Paquier and Masahiko Sawada

Discussion: https://postgr.es/m/CAPpHfdtohPdQ9rc5mdWjxq+3VsBNw534KV_5O65dTQrSdVJNgw@mail.gmail.com