Ensure system_cfg read before ds net config on Oracle (SC-720)

[TheRealFalcon]

Proposed Commit Message

Ensure system_cfg read before ds net config on Oracle

In 2c52e6e88b19f5db8d55eb7280ee27703e05d75f, the order of
reading network config was changed for Oracle due to initramfs
needing to take lower precedence than the datasource. However,
this also bumped system_cfg to a lower precedence than ds, which
means that any network configuration specified in /etc/cloud will not
be applied. system_cfg should instead be moved above ds so network
configuration in /etc/cloud takes precedence.

LP: #1956788

Additional Context

2c52e6e

Test Steps

Boot an Oracle instance using the Oracle datasource.
Create /etc/cloud/cloud.cfg.d/99-disable-network-config.cfg with contents network: {config: disabled}
rm /etc/netplan/50-cloud-init.yaml (or rename it if you need it)
cloud-init clean --logs && cloud-init init --local
Without patch, /etc/netplan/50-cloud-init.yaml should get written. With patch, it won't be written and logs should show no network written.

I can also include an Oracle-specific integration test, but wanted to get the PR up sooner rather than later.

Checklist:

• My code follows the process laid out in the documentation
• I have updated or added any unit tests accordingly
• I have updated or added any documentation accordingly

[blackboxsw]

Trying to run through an Oracle test now to confirm expected behavior.

[blackboxsw]

LGTM.
confirmed upgrade behavior without restart via sudo cloud-init init --local; sudo cloud-init init allows OracleDatasource to see the disabled config. Same across system reboot network is no longer rendered and instance remains accessible via ssh.

ubuntu@instance-20220115-0946:~$ grep 'disabled by' /var/log/cloud-init.log 
2022-01-15 17:44:55,657 - stages.py[DEBUG]: network config disabled by system_cfg
2022-01-15 17:44:55,657 - stages.py[INFO]: network config is disabled by system_cfg
2022-01-15 17:44:56,102 - stages.py[DEBUG]: network config disabled by system_cfg
2022-01-15 17:44:56,102 - stages.py[INFO]: network config is disabled by system_cfg
...
ubuntu@instance-20220115-0946:~$ ls /etc/netplan/
ubuntu@instance-20220115-0946:~$
ubuntu@instance-20220115-0946:~$ cloud-init status --long
status: done
time: Sat, 15 Jan 2022 17:52:25 +0000
detail:
DataSourceOracle
ubuntu@instance-20220115-0946:~$ grep Trace /var/log/cloud-init.log 
ubuntu@instance-20220115-0946:~$

cloud-init can be re-enabled for networking on oracle by sudo rm /etc/cloud/cloud.cfg.d/99-disable-network-config.cfg