Fix test_oneshot_on_usr2_error to reset the buffer before doing the s…

…econd connection test.

tests/test_manhole.py

@@ -395,6 +395,7 @@ def test_oneshot_on_usr2_error(self):
                 self._wait_for_strings(proc.read, TIMEOUT, 'Waiting for new connection')
                 self.assertManholeRunning(proc, uds_path, oneshot=True, extra=lambda sock: sock.send(b"raise SystemExit()\n"))
 
+                proc.reset()
                 proc.signal(signal.SIGUSR2)
                 self._wait_for_strings(proc.read, TIMEOUT, '/tmp/manhole-')
                 uds_path = re.findall("(/tmp/manhole-\d+)", proc.read())[0]