instance-data: fallback to instance-data.json if sensitive is absent.
On cloud-init upgrade path from 18.3 to 18.4 cloud-init changed how
instance-data is written. Cloud-init changes instance-data.json from root
read-only to redacted world-readable content, and provided a separate
unredacted instance-data-sensitive.json which is read-only root.
Since instance-data is only rewritten from cache on
reboot, the query and render tools needed fallback to use the 'old'
instance-data.json if the new sensitive file isn't yet present.
This avoids error messages from tools about an absebt
/run/instance-data-sensitive.json file.
azure: Add apply_network_config option to disable network from IMDS
Azure generates network configuration from the IMDS service and removes
any preexisting hotplug network scripts which exist in Azure cloud images.
Add a datasource configuration option which allows for writing a default
network configuration which sets up dhcp on eth0 and leave the hotplug
handling to the cloud-image scripts.
To disable network-config from Azure IMDS, add the following to
/etc/cloud/cloud.cfg.d/99-azure-no-imds-network.cfg:
datasource:
Azure:
apply_network_config: False
