Test system LEDs.

This change includes:
   - Added test cases to turn on/off heartbeat, beep and
     identify LEDs.
   - Added keywords to get and set physical LED state.
   - Skipped these test case for Witherspoon system.

Resolves openbmc/openbmc-test-automation#404

Change-Id: I64c939d50852e4b627ad8bf559b75da4f95237a1
Signed-off-by: Rahul Maheshwari <rahulmaheshwari@in.ibm.com>
diff --git a/test_lists/skip_test_witherspoon b/test_lists/skip_test_witherspoon
index 474715b..3072f20 100644
--- a/test_lists/skip_test_witherspoon
+++ b/test_lists/skip_test_witherspoon
@@ -43,3 +43,5 @@
 -e eSEL_Logging
 #openbmc/openbmc-test-automation/issues/396
 -e NetworkManager
+# System LED test are NA for Witherspoon system.
+-e System_LED