added loopback test mode

linux/boardtest/LibgpiodTest.h

@@ -12,6 +12,13 @@
  */
 class LibgpiodTest: public TestTask {
 public:
+    enum TestCases {
+        READ = 0,
+        LOOPBACK = 1
+    };
+
+    TestCases testCase;
+
     LibgpiodTest(object_id_t objectId, object_id_t gpioIfobjectId, GpioCookie* gpioCookie);
     virtual ~LibgpiodTest();