fmq_unit_tests: Write a log msg before tracking open FDs

We open a socket and a pstore file when we log. Make sure that happens
before we start looking for leaked FDs in case this test case is run by
itself.

Test: atest fmq_unit_tests
Bug: none

Change-Id: I528b2fb2b40b5fe4859f4057af91396c538ee97d