test: replace CONFIG+=insignificant_test with QEXPECT_FAIL for tst_qftp

This autotest failure is entirely stable, so QEXPECT_FAIL should be used
instead of insignificant_test.

Task-number: QTBUG-20687
Change-Id: I0444e725b436fe93d30cbe54edc673594ca9b9fe
Reviewed-on: http://codereview.qt.nokia.com/2486
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Kalle Lehtonen <kalle.ju.lehtonen@nokia.com>

tests/auto/qftp/qftp.pro

@@ -18,5 +18,3 @@ wince*: {
 } else {
    DEFINES += SRCDIR=\\\"$$PWD/\\\"
 }
-
-CONFIG+=insignificant_test

tests/auto/qftp/tst_qftp.cpp

@@ -378,6 +378,8 @@ void tst_QFtp::connectToUnresponsiveHost()
     a lot of other stuff in QFtp, so we just expect this test to fail on Windows.
     */
     QEXPECT_FAIL("", "timeout not working due to strange Windows socket behaviour (see source file of this test for explanation)", Abort);
+#else
+    QEXPECT_FAIL("", "QTBUG-20687", Abort);
 #endif
     QVERIFY2(! QTestEventLoop::instance().timeout(), "Network timeout longer than expected (should have been 60 seconds)");