test: fix flaky test_cancel_from_master

We did not wait long enough for the tested process to set their signal
handler, as we can see on test history [1], this test fails often when
running on test node.

It always pass when I run locally, but if I adjust the _tmasterpoll
patch set to 0.01 second, it fails the same way.

1: https://erp5.nexedi.net/test_result_module/20220616-13A460D9B/2/TestResultLine_viewResultHistory

/reviewed-on nexedi/nxdtest!17

nxdtest/nxdtest_test.py

@@ -342,7 +342,7 @@ def test_cancel_from_master(run_nxdtest, capsys, distributor_with_cancelled_test
     # nxdtest polls every 5 minutes, but in test we don't want to wait so long.
     # set master poll interval to small, but enough time for spawned hang to
     # setup its signal handler.
-    mocker.patch('nxdtest._tmasterpoll', 0.1*time.second)
+    mocker.patch('nxdtest._tmasterpoll', 1*time.second)
 
     hang = "%s/testprog/hang" % (dirname(__file__),)
     run_nxdtest(