Skip unstable autotest

tst_QSharedMemory::simpleProcessProducerConsumer is on the top list of
unstable autotests. Disabling it for now.

Task-number: QTBUG-25655
Change-Id: Ib297b3382b736794bab6cdb668103bef74a55d8c
Reviewed-by: Samuel Rødal <samuel.rodal@digia.com>
Reviewed-by: Lars Knoll <lars.knoll@digia.com>

tests/auto/corelib/kernel/qsharedmemory/test/tst_qsharedmemory.cpp

@@ -748,6 +748,8 @@ void tst_QSharedMemory::simpleProcessProducerConsumer()
 {
     QFETCH(int, processes);
 
+    QSKIP("This test is unstable: QTBUG-25655");
+
     rememberKey("market");
 
     QProcess producer;