Fix tests for RabbitMQ password hash

Summary:
This is a follow-up for 79c7da764e62.

Ref T752.

Test Plan: python3 -m unittest modules/test_rabbitmq.py

Reviewers: dereckson

Reviewed By: dereckson

Maniphest Tasks: T752

Differential Revision: https://devcentral.nasqueron.org/D3347