nocloud: accept dict-of-strings public-keys format

Some sources serialise public-keys as a dict of {name: key-string}
rather than {name: {'openssh-key': key-string}}. KubeVirt's
accessCredentials sshPublicKey noCloud propagation does this, defining
NoCloudMetadata.PublicSSHKeys as map[string]string [1] and assigning
it directly in readCloudInitNoCloudMetaData [2]. The current third
branch of get_public_keys() then calls .get('openssh-key') on a string
value and raises "'str' object has no attribute 'get'". Accept both
shapes.

[1] https://github.com/kubevirt/kubevirt/blob/623bf15e7553875860ece1a382a9e35bfbd61a26/pkg/cloud-init/cloud-init.go#L84
[2] https://github.com/kubevirt/kubevirt/blob/623bf15e7553875860ece1a382a9e35bfbd61a26/pkg/cloud-init/cloud-init.go#L402-L408

AI-assisted contribution: I reviewed the change and submit it under
the DCO terms at https://github.com/cloudbase/cloudbase-init/blob/master/DCO#L16
(clause (a) — the contribution is mine).

Signed-off-by: mattia-eleuteri <mattia@hidora.io>

Author: mattia-eleuteri

cloudbaseinit/metadata/services/nocloudservice.py

@@ -695,7 +695,13 @@ def get_public_keys(self):
         if isinstance(raw_ssh_keys, list):
             return raw_ssh_keys
 
-        return [raw_ssh_keys[key].get('openssh-key') for key in raw_ssh_keys]
+        keys = []
+        for value in raw_ssh_keys.values():
+            if isinstance(value, str):
+                keys.append(value)
+            else:
+                keys.append(value.get('openssh-key'))
+        return keys
 
     def get_network_details(self):
         debian_net_config = self._get_meta_data().get('network-interfaces')

cloudbaseinit/tests/metadata/services/test_nocloudservice.py

@@ -516,6 +516,19 @@ def test_get_public_keys_alt_fmt(self, mock_get_metadata):
         result = self._config_drive.get_public_keys()
         self.assertEqual(result, expected_result)
 
+    @mock.patch(MODULE_PATH + '.NoCloudConfigDriveService._get_meta_data')
+    def test_get_public_keys_dict_of_strings(self, mock_get_metadata):
+        fake_key0 = 'ssh-rsa AAAA0 user0@host'
+        fake_key1 = 'ssh-rsa AAAA1 user1@host'
+        mock_get_metadata.return_value = {
+            'public-keys': {
+                'key0': fake_key0,
+                'key1': fake_key1,
+            }
+        }
+        result = sorted(self._config_drive.get_public_keys())
+        self.assertEqual(result, sorted([fake_key0, fake_key1]))
+
     @ddt.data(('', ('V2 network metadata is empty', None)),
               ('1', ('V2 network metadata is not a dictionary', None)),
               ('{}', ('V2 network metadata is empty', None)),