Original author: Grigorii Demidov <grigorii.demidov@nic.cz>

In our CI, this test ocassionally fails. This is most likely due to
delays in kernel processing due to many virtualization layers coupled
with massive paralelization of tests.

Closes #427

Attempt to increase test stability in CI under high load.

Docker uses 32768 - 61000 as ephemeral ports. Don't use
this range for kresd to avoid collisions.