Use /tmp to test eq operator of qdir

The test checks if two paths test equal if they are pointing to the same
place, but one of them is not a canonical path.
Example of such paths: /tmp/.. and /

The test assumes that /usr is an existing directory on platforms other
than win, haiku and android.
The reason /usr is used instead of /tmp is that /tmp is a symlink on
macos and that interferes with the test (as described in 0b67ad9d).
However /usr does not exist on VxWorks (unless created by the user).

/tmp can (and is in our CI env) enabled by turning on the
INCLUDE_TMP_DIR component.

Solve the problem by using /tmp instead of /usr on vxworks.

Pick-to: 6.7 6.8
Task-number: QTBUG-115777
Change-Id: I98b0d46d1b879f404c0b5bd655031e7c3f19ba33
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

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

@@ -2285,6 +2285,8 @@ void tst_QDir::equalityOperator_data()
     QString pathinroot("/system/..");
 #elif defined(Q_OS_HAIKU)
     QString pathinroot("/boot/..");
+#elif defined(Q_OS_VXWORKS)
+    QString pathinroot("/tmp/..");
 #else
     QString pathinroot("/usr/..");
 #endif