1. Make it support multiple servers. 

https://chrome-internal-review.googlesource.com/c/chromeos/chromeos-admin/+/656193.

2. Use atest to add multiple servers to skylab_inventory:

This step also needs to pass-in '--submit' to make it automatically submitted.

3. Whitelist multiple servers. With current site_utils/sync_cloudsql_access.py, it depends on step 2 to take effect (I assume it's immediately).

I'd like site_utils/sync_cloudsql_access.py to only add servers to whitelist, given the assumption that the existing whitelist is correct. But after Issue 868052 is fixed, this won't be a problem anymore. Step 3 is not needed.