Sort the gerrit failed event bug urls map for predictive tests

The bug_urls_map method is actually returning a list so just sort the
list and fix the tests that are racing due to random hashseed issues
with the dict.

This also updates the docstring which was incorrect before.

Related-Bug: #1348818

Change-Id: I13ca69b3e685083d4ced2b054e0d42a440259854