Add system example tests

examples/system/task_watchdog/example_test.py

@@ -0,0 +1,18 @@
+from __future__ import unicode_literals
+import ttfw_idf
+
+
+@ttfw_idf.idf_example_test(env_tag='Example_WIFI')
+def test_examples_task_watchdog(env, extra_data):
+
+    dut = env.get_dut('task_watchdog', 'examples/system/task_watchdog')
+    dut.start_app()
+
+    dut.expect_all('Initialize TWDT',
+                   'Delay for 10 seconds', timeout=30)
+    dut.expect_all('Unsubscribing and deleting tasks',
+                   'Complete', timeout=20)
+
+
+if __name__ == '__main__':
+    test_examples_task_watchdog()