Use naming convention to infer VLAN tagging

Any interface not matching the convention: <interface>.<vlan id> will be
assumed to untagged when generating the config drive. The link type will
be set to `phy` in `network_data.json` instead of `vlan`. This prevents
invalid config drive configuration from being generated.

Change-Id: I00e7615581c7a214e0ee8e8f04cacdbb3ea4131a
Story: 2009910
Task: 44736

kayobe/plugins/filter/networks.py

@@ -595,7 +595,7 @@ def net_configdrive_network_device(context, name, inventory_hostname=None):
     bootproto = net_bootproto(context, name, inventory_hostname)
     mtu = net_mtu(context, name, inventory_hostname)
     vlan = net_vlan(context, name, inventory_hostname)
-    if vlan:
+    if vlan and '.' in device:
         backend = [device.split('.')[0]]
     else:
         backend = None
@@ -608,7 +608,7 @@ def net_configdrive_network_device(context, name, inventory_hostname=None):
         'mtu': mtu,
         'backend': backend,
     }
-    if vlan:
+    if backend:
         interface['type'] = 'vlan'
     interface = {k: v for k, v in interface.items() if v is not None}
     return interface

releasenotes/notes/fixes-keyerror-vlan-link-c177cf719e070df6.yaml

+---
+fixes:
+  - |
+    Fixes an issue with config drive generation for infrastructure and seed VMs
+    when using untagged interfaces. The symptom of this issue is that kayobe
+    cannot login to the instance. If you check the libvirt console log, you
+    will see ``KeyError: 'vlan_link'``. See `story 2009910
+    <https://storyboard.openstack.org/#!/story/2009910>`__ for details.