FreeCADTest.py invokes sys.exit() instead of the more aggressive os._exit()

With the ability to now pass the <exitCode> from sys.exit() up the
call stack to the shell, FreeCADTest.py should use sys.exit() instead
of the more aggressive os._exit() method that does not allow for
post-exception cleanup.

src/App/FreeCADTest.py

@@ -32,10 +32,10 @@
 
 Log ("FreeCAD test running...\n\n")
 
-import TestApp, os
+import TestApp, sys
 
 testResult = TestApp.TestText("TestApp.All")
 
 Log ("FreeCAD test done\n")
 
-os._exit(0 if testResult.wasSuccessful() else 1)
+sys.exit(0 if testResult.wasSuccessful() else 1)