azure: /run/cloud-init/cloud-id broken symlink across reboot.

cloud-init 22.4.2

On Azure, datasource details change across reboot cloud-init incorrectly removes /run/cloud-init/cloud-id-azure symlink.

2022-12-07 04:14:17,920 - util.py[DEBUG]: Creating symbolic link from '/run/cloud-init/cloud-id' => '/run/cloud-init/cloud-id-azure'
2022-12-07 04:14:17,920 - util.py[DEBUG]: Attempting to remove /run/cloud-init/cloud-id-azure

# FRESH LAUNCH
ubuntu@test-focal:~$ ls -l /run/cloud-init/cloud-id
lrwxrwxrwx 1 root root 30 Dec 7 04:10 /run/cloud-init/cloud-id -> /run/cloud-init/cloud-id-azure
ubuntu@test-focal:~$ grep cloud-id /var/log/cloud-init.log
2022-12-07 04:10:34,734 - util.py[DEBUG]: Writing to /run/cloud-init/cloud-id-azure - wb: [644] 6 bytes
2022-12-07 04:10:34,735 - util.py[DEBUG]: Creating symbolic link from '/run/cloud-init/cloud-id' => '/run/cloud-init/cloud-id-azure'

# ACROSS REBOOT

ubuntu@test-focal:~$ ls -l /run/cloud-init/cloud-id
lrwxrwxrwx 1 root root 30 Dec 7 04:14 /run/cloud-init/cloud-id -> /run/cloud-init/cloud-id-azure

2022-12-07 04:14:17,920 - util.py[DEBUG]: Writing to /run/cloud-init/cloud-id-azure - wb: [644] 6 bytes
2022-12-07 04:14:17,920 - util.py[DEBUG]: Creating symbolic link from '/run/cloud-init/cloud-id' => '/run/cloud-init/cloud-id-azure'
2022-12-07 04:14:17,920 - util.py[DEBUG]: Attempting to remove /run/cloud-init/cloud-id-azure

It looks like the symlink cleanup logic introduced in https://github.com/canonical/cloud-init/commit/217ef6ba6c52788f4363b998b6da08863fea5cd9 (which was released in cloud-init v. 21.4) doesn't do a proper comparison of previous-datasource to current datasource

Debug logs added to https://github.com/canonical/cloud-init/blob/main/cloudinit/sources/__init__.py#L443 shows that we are comparing the incorrect source file /root/cloud-init/cloud-id versus actually comparing the cloud-specific symlink name /run/cloud-init/cloud-id-<cloud>, resulting in a removal of the cloud-specific link name across reboot.

2022-12-07 04:25:58,162 - __init__.py[WARNING]: previous_cloud_id_file /run/cloud-init/cloud-id-azure != cloud_id_file /run/cloud-init/cloud-id

Likely all we need is a correction in logic like the following:
diff --git a/cloudinit/sources/__init__.py b/cloudinit/sources/__init__.py
index 85e094ac5..3fb08ead2 100644
--- a/cloudinit/sources/__init__.py
+++ b/cloudinit/sources/__init__.py
@@ -439,8 +439,9 @@ class DataSource(CloudInitPickleMixin, metaclass=abc.ABCMeta):
             prev_cloud_id_file = os.path.realpath(cloud_id_file)
         else:
             prev_cloud_id_file = cloud_id_file
- util.sym_link(f"{cloud_id_file}-{cloud_id}", cloud_id_file, force=True)
- if prev_cloud_id_file != cloud_id_file:
+ new_cloud_id_file = f"{cloud_id_file}-{cloud_id}"
+ util.sym_link(new_cloud_id_file, cloud_id_file, force=True)
+ if prev_cloud_id_file != new_cloud_id_file:
             util.del_file(prev_cloud_id_file)
         write_json(json_sensitive_file, processed_data, mode=0o600)
         json_file = self.paths.get_runpath("instance_data")