reuse load_minigraph in sonic utilities in config-setup and updategraph

[lguohan]

Description
in #3227

can't the command "config reload or config load -m <>" be used ?
This code here replicated steps from load_minigraph() function in sonic-utilities/config/main.py
If someone updates that part, they should also be updating it here. Doing it like this opens doorway to config load getting out of sync between "config load" and through ztp

Steps to reproduce the issue:
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Describe the results you received:

Describe the results you expected:

Additional information you deem important (e.g. issue happens only occasionally):

**Output of `show version`:**

```
(paste your output here)
```

**Attach debug file `sudo generate_dump`:**

```
(paste your output here)
```

[lguohan]

@rajendra-dendukuri