tst_QTcpSocket::suddenRemoteDisconnect - fix flakyness

This test starts two processes - server and client - and requires
an external executable ('stressTest'). In .pro file we have SUBDIRS
containing both 'test' (test itself) and 'stressTest' (client/server app),
but there is no explicit dependency and as result we run the test before
we build 'stressTest' thus failing to start those processes. This patch makes
'test' dependent on 'stressTest'.

Task-number: QTBUG-36629
Change-Id: I286b08bcff86b9afc4bbee87a75e887527eaf5f2
Reviewed-by: Gatis Paeglis <gatis.paeglis@qt.io>

tests/auto/network/socket/qtcpsocket/qtcpsocket.pro

@@ -1,6 +1,8 @@
 TEMPLATE = subdirs
 
 SUBDIRS = test
-!vxworks: SUBDIRS += stressTest
-
+!vxworks{
+SUBDIRS += stressTest
+test.depends = stressTest
+}
 requires(qtConfig(private_tests))