skip pfcwd if disabled in golden_config (#178)

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## Skip pfcwd config if it's disabled in golden config

In `sudo config load_minigraph --override_config -y`, it will call `pfcwd start_default` by default.
```
Running command: /usr/local/bin/sonic-cfggen -H -m -j /etc/sonic/init_cfg.json --write-to-db
......
Running command: pfcwd start_default
Running command: config override-config-table /etc/sonic/golden_config_db.json
```

When golden_config_db.json has `"default_pfcwd_status": disable`, pfcwd should not be generated in the config.
However, in current code, when `pfcwd start_default` is called, the `default_pfcwd_status` is still using the value in `init_cfg.json` which is `enable`. So, pfcwd configuration is still generated even though it's not needed.

#### What I did
Disable default_pfcwd_status for all lossy platform.

#### How I did it
Check `default_pfcwd_status` in `golden_config_db.json` and skip `pfcwd start_default` if it's disabled.

#### How to verify it

Run deploy-mg on all lossy platform

#### Previous command output (if the output of a command-line utility has changed)

#### New command output (if the output of a command-line utility has changed)

Author: mssonicbld

config/main.py

@@ -2101,7 +2101,16 @@ def load_minigraph(db, no_service_restart, traffic_shift_away, override_config,
     # get the device type
     device_type = _get_device_type()
     if device_type != 'MgmtToRRouter' and device_type != 'MgmtTsToR' and device_type != 'BmcMgmtToRRouter' and device_type != 'EPMS':
-        clicommon.run_command(['pfcwd', 'start_default'], display_cmd=True)
+        # default behavior to call pfcwd start_default for all platforms
+        default_pfcwd_status = 'enable'
+        if override_config and config_to_check:
+            # If pfcwd is disabled in the golden config, skip starting pfcwd
+            # This is needed for platform which doesn't support lossless traffic.
+            override_metadata = config_to_check.get('DEVICE_METADATA', {}).get('localhost', {})
+            if 'default_pfcwd_status' in override_metadata:
+                default_pfcwd_status = override_metadata['default_pfcwd_status'].lower()
+        if default_pfcwd_status == 'enable':
+            clicommon.run_command(['pfcwd', 'start_default'], display_cmd=True)
 
     # Write latest db version string into db
     db_migrator = '/usr/local/bin/db_migrator.py'