TeeTest.calculateTimers unittest failing

since [#360 (closed),!305 (merged)] was merged there is one unit test that is keep failing.

https://jenkins.isc.org/job/kea-master/348/testReport/junit/(root)/TeeTest/Multi_node_testing_loop___fedora27_32___results___calculateTimers/

it's failing just on fedora 27 32 bit. fedora27-32-2