test: remove `sleep` usage in `test-nointerrupt.t` (issue6271)

We move from sleep based synchronisation to file creation based synchronisation.

Sleeps is the path to the dark side.
Sleeps leads to flakiness.
Flakiness leads to anger.
Anger leads to hate.
Hate leads to suffering.

--HG--
branch : stable
16 jobs for topic/stable/issue6271 in 58 minutes and 19 seconds (queued for 4 minutes and 19 seconds)
Status Job ID Name Coverage
  Tests
manual check-pytype-py3 #227546
allowed to fail manual
passed checks-py2 #227533

00:04:37

passed checks-py3 #227534

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passed rust-cargo-test-py2 #227535

00:03:26

passed rust-cargo-test-py3 #227536

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passed test-py2 #227537

00:23:10

passed test-py2-chg #227544

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passed test-py2-pure #227539

00:27:41

passed test-py2-rust #227541

00:27:19

passed test-py3 #227538

00:13:49

passed test-py3-chg #227545

00:07:45

passed test-py3-pure #227540

00:17:19

passed test-py3-rhg #227543

00:15:42

passed test-py3-rust #227614

00:21:22

canceled test-py3-rust #227542

01:38:40

 
  Phabricator
passed phabricator-refresh #227547

00:00:23