Reproduce bug in qrexec tests

The qrexec tests are broken and fail intermittently.  This patch makes
the bug obvious: by adding a sleep, it causes the test to fail right
away, reliably.

qubes/tests/integ/qrexec.py

@@ -496,7 +496,7 @@ def test_080_qrexec_service_argument_allow_default(self):
         self.create_remote_file(
             self.testvm2,
             "/etc/qubes-rpc/test.Argument",
-            '/usr/bin/printf %s "$1"',
+            'sleep 20 && /usr/bin/printf %s "$1"',
         )
         with self.qrexec_policy("test.Argument", self.testvm1, self.testvm2):
             stdout, stderr = self.loop.run_until_complete(