Fix setupInstanceFirewall function for accounts with default firewall

[zliang-akamai]

📝 Description

For some accounts with default firewall setting, the Linode will be created behind the default firewall even if firewall_id is not configured for the Linode creation options. Updating the test function to add the firewall_id in the creation options to override the default firewall. Otherwise, we won't be able to add the Linode to the test firewall after creation because it would already be behind the default firewall.

Other changes:

1. Migrate manual deferral cleanup function calls with t.Cleanup for setupInstanceFirewall.

✔️ How to Test

If you would like to add a default firewall to your account before verifying the test case, you can call the API with cURL with the default firewall ID for each Linode resource as below.

WARNING:
This action cannot be undone. Once you configure the default firewall, you can only change it to another firewall; you cannot unset it.
And it's unclear whether having a default firewall will affect some other tests.

curl --request PUT \   
     --url https://api.linode.com/v4beta/networking/firewalls/settings \ 
     --header 'accept: application/json' \
     --header "authorization: Bearer $TOKEN" \
     --header 'content-type: application/json' \
     --data '
{
    "default_firewall_ids": { 
        "public_interface": 1629606,
        "vpc_interface": 1629606,
        "linode": 1629606,
        "nodebalancer": 1629606
    }               
}

'

make TEST_ARGS="-run TestInstanceFirewalls_List" fixtures

[yec-akamai]

Thanks for putting up the fix!