Fix Bifrost host variable file generation

In deployments without an IPv4 gateway defined, for example when behind
a proxy, Bifrost host variable file generation was failing. Fix by
allowing ipv4_gateway to be set to an empty string, which is supported
in Bifrost.

Closes-Bug: #2133489
Change-Id: I988810541b4620ac196d216bf54896a774282fdd
Signed-off-by: Pierre Riteau <[email protected]>
(cherry picked from commit fa13678)

Author: priteau

ansible/kolla-bifrost-hostvars.yml

@@ -26,7 +26,7 @@
       # If the admin network does not have a gateway defined and seed SNAT is
       # enabled, use the seed as a gateway to allow external access until other
       # networks have been configured. Otherwise, do not set any gateway.
-      ipv4_gateway: "{{ (admin_oc_net_name | net_gateway) or (admin_oc_net_name | net_ip(seed_host) if seed_enable_snat | bool) }}"
+      ipv4_gateway: "{{ (admin_oc_net_name | net_gateway) or (admin_oc_net_name | net_ip(seed_host) if seed_enable_snat | bool) or '' }}"
       ipv4_nameserver: "{{ resolv_nameservers }}"
       network_mtu: "{{ admin_oc_net_name | net_mtu or '1500' }}"
       vlan_id: "{{ '' if admin_oc_net_name == provision_oc_net_name else (admin_oc_net_name | net_vlan) }}"

releasenotes/notes/bug-2133489-1b83b7e24655caff.yaml

@@ -0,0 +1,5 @@
+---
+fixes:
+  - |
+    Fixes generation of Bifrost host variable files when ``ipv4_gateway`` is
+    undefined. `LP#2133489 <https://bugs.launchpad.net/kayobe/+bug/2133489>`__