UT IOSignalTest.mixedSignals fails on CentOS 7

It passes on 1.9.4 and below, so might be caused by IOSignal changes done under #1657 (closed).

It passes on all versions on CentOS 8.

[ RUN      ] IOSignalTest.mixedSignals
io_service_signal_unittests.cc:274: Failure
Expected equality of these values:
  sigint_cnt
    Which is: 21
  (stop_at_count_/3)
    Which is: 7
io_service_signal_unittests.cc:275: Failure
Expected equality of these values:
  sigusr1_cnt
    Which is: 0
  (stop_at_count_/3)
    Which is: 7
io_service_signal_unittests.cc:276: Failure
Expected equality of these values:
  sigusr2_cnt
    Which is: 0
  (stop_at_count_/3)
    Which is: 7
[  FAILED  ] IOSignalTest.mixedSignals (24 ms)

The following UTs are in the same boat. They also fail consistently on CentOS 7:

• HAServiceTest.sendUpdatesControlResultErrorMultiThreading
• HAServiceTest.sendUpdatesControlResultUnauthorizedMultiThreading
• NameChangeUDPTest.roundTripTest

If possible, it would be nice to fix these as part of this issue.

Reproduced on a CentOS 7.9: config.report