Fix asyncWaitForStdoutAndRun error message

Unfortunately `require.Fail` first string argument isn't the format
string, it is the second one. The first one is general error message
string. Same goes for Failf, which just happens to require the actual
format message as argument.

cmd/integration_test.go

@@ -700,7 +700,7 @@ func asyncWaitForStdoutAndRun(
 		ts.outMutex.Unlock()
 		t.Log(stdOut)
 		require.FailNow(
-			t, "did not find the text '%s' in the process stdout after %d attempts (%s)",
+			t, "expected output not found", "did not find the text '%s' in the process stdout after %d attempts (%s)",
 			expText, attempts, time.Duration(attempts)*interval,
 		)
 	}()