The test "a host that stops answering is looked at in the background" no longer fails on Linux

When asked whether a card could take a clone, Obeya answered at once and started its look at the host in the background, as it should. The test, though, counted every ssh call the moment it started and expected none yet. On Linux the background ssh process often started before the test read the count (12 expected, 13 found); on the Mac it usually started just after. So the server behaved correctly. The test measured process start-up speed instead of what it was meant to check.

The test now checks what it means: the answer comes before any look at the host has answered (right after the question, the host does not count as unreachable yet). The rest is unchanged: the looks find the host gone, and later questions don't ask it again until a minute has passed. If the server ever waited for the host, the new check would fail; I tried that with a deliberate pause.