[config]: Add file check before load_minigraph command

[stcheng]

This will prevent config load_minigraph fail during the middle of the command execution.

Signed-off-by: Shu0T1an ChenG [email protected]

[stcheng]

yes. I think the use-case for load_minigraph is that the config_db.json file is not easy to modify while right now the minigraph is the source of the 'original configuration' for the switch.

[qiluo-msft]

run_command("config qos reload", display_cmd=True)

Since 'qos' is a local function, why we don't directly call it?

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Refers to: config/main.py:344 in ef57bac. [](commit_id = ef57bac77bcdbf0e04b0d2b0295484ee524b2331, deletion_comment = False)