Fix issue: exception occurred during chassis object being destroyed (s…

…onic-net#7446)

The following error message is observed during chassis object being destroyed

"Exception ignored in: <function Chassis.__del__ at 0x7fd22165cd08>
Traceback (most recent call last):
  File "/usr/local/lib/python3.7/dist-packages/sonic_platform/chassis.py", line 83, in __del__
ImportError: sys.meta_path is None, Python is likely shutting down
The chassis tries to import deinitialize_sdk_handle during being destroyed for the purpose of releasing the sdk_handle.
However, importing another module during shutting down can cause the error because some of the fundamental infrastructures are no longer available."

This error occurs when a chassis object is created and then destroyed in the Python shell.

- How I did it
To fix it, record the deinitialize_sdk_handle in the chassis object when sdk_handle is being initialized and call the deinitialize handler when the chassis object is being destroyed

- How to verify it
Manually test.

platform/mellanox/mlnx-platform-api/sonic_platform/chassis.py

@@ -73,16 +73,16 @@ def __init__(self):
         self.sfp_event_initialized = False
         self.reboot_cause_initialized = False
         self.sdk_handle = None
+        self.deinitialize_sdk_handle = None
         logger.log_info("Chassis loaded successfully")
 
 
     def __del__(self):
         if self.sfp_event_initialized:
             self.sfp_event.deinitialize()
 
-        if self.sdk_handle:
-            from sonic_platform.sfp import deinitialize_sdk_handle
-            deinitialize_sdk_handle(self.sdk_handle)
+        if self.deinitialize_sdk_handle:
+            self.deinitialize_sdk_handle(self.sdk_handle)
 
 
     def initialize_psu(self):
@@ -140,10 +140,12 @@ def initialize_sfp(self):
 
     def get_sdk_handle(self):
         if not self.sdk_handle:
-            from sonic_platform.sfp import initialize_sdk_handle
+            from sonic_platform.sfp import initialize_sdk_handle, deinitialize_sdk_handle
             self.sdk_handle = initialize_sdk_handle()
             if self.sdk_handle is None:
                 logger.log_error('Failed to open SDK handle')
+            else:
+                self.deinitialize_sdk_handle = deinitialize_sdk_handle
         return self.sdk_handle