add set get uid led api (sonic-net#369)

* add set get uid led api

* add test case to improve coverage

Author: daxia16

sonic_platform_base/chassis_base.py

@@ -546,6 +546,33 @@ def get_status_led(self):
         """
         raise NotImplementedError
 
+    ##############################################
+    # System LED methods
+    ##############################################
+
+    def set_uid_led(self, color):
+        """
+        Sets the state of the system UID LED
+
+        Args:
+            color: A string representing the color with which to set the
+                   system UID LED
+
+        Returns:
+            bool: True if system LED state is set successfully, False if not
+        """
+        raise NotImplementedError
+
+    def get_uid_led(self):
+        """
+        Gets the state of the system UID LED
+
+        Returns:
+            A string, one of the valid LED color strings which could be vendor
+            specified.
+        """
+        raise NotImplementedError
+
     ##############################################
     # Other methods
     ##############################################

tests/chassis_base_test.py

@@ -16,3 +16,21 @@ def test_reboot_cause(self):
         assert(chassis.REBOOT_CAUSE_HARDWARE_BUTTON == "Push button")
         assert(chassis.REBOOT_CAUSE_HARDWARE_RESET_FROM_ASIC == "Reset from ASIC")
         assert(chassis.REBOOT_CAUSE_NON_HARDWARE == "Non-Hardware")
+
+    def test_chassis_base(self):
+        chassis = ChassisBase()
+        not_implemented_methods = [
+                [chassis.get_uid_led],
+                [chassis.set_uid_led, "COLOR"],
+            ]
+
+        for method in not_implemented_methods:
+            exception_raised = False
+            try:
+                func = method[0]
+                args = method[1:]
+                func(*args)
+            except NotImplementedError:
+                exception_raised = True
+
+            assert exception_raised