Mark QNetworkReply test as unstable

QTBUG-21102 is currently blocking integration of several commits.
Marking the test as unstable until the bug has been fixed.

Change-Id: I9b630767fd1aa4369564f5e90c63e850808385e1
Reviewed-on: http://codereview.qt.nokia.com/3584
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Martin Petersson <Martin.Petersson@nokia.com>

tests/auto/qnetworkreply/test/test.pro

@@ -3,6 +3,8 @@ QT -= gui
 SOURCES  += ../tst_qnetworkreply.cpp
 TARGET = ../tst_qnetworkreply
 
+qpa:contains(QT_CONFIG,xcb): CONFIG+=insignificant_test  # unstable, QTBUG-21102
+
 win32 {
   CONFIG(debug, debug|release) {
     TARGET = ../../debug/tst_qnetworkreply