Android: Fix tst_QDir::cdBelowRoot()

The /tmp directory doesn't exist on Android, and the test needs
a directory that it can cd into which is one level above root.
So we just use /system which should be available on all devices.

Change-Id: I8e6a15f278429491fd871f87af497e5d7184ddf8
Reviewed-by: BogDan Vatra <bogdan@kde.org>

tests/auto/corelib/io/qdir/tst_qdir.cpp

@@ -2176,7 +2176,11 @@ void tst_QDir::cdNonreadable()
 
 void tst_QDir::cdBelowRoot()
 {
-#if defined (Q_OS_UNIX)
+#if defined (Q_OS_ANDROID)
+#define ROOT QString("/")
+#define DIR QString("/system")
+#define CD_INTO "system"
+#elif defined (Q_OS_UNIX)
 #define ROOT QString("/")
 #define DIR QString("/tmp")
 #define CD_INTO "tmp"