vault: Use internal FQDN for barbican -> Vault communication

Typically the certificate is only valid for the FQDN. This will not
cause a problem usually because the internal API generally uses the VIP
directly rather than an FQDN.

Author: markgoddard

doc/source/configuration/vault.rst

@@ -347,7 +347,7 @@ Configure Barbican
       enabled_secretstore_plugins=vault_plugin
 
       [vault_plugin]
-      vault_url = https://{{ kolla_internal_vip_address }}:8200
+      vault_url = https://{{ kolla_internal_fqdn }}:8200
       use_ssl = True
       {% raw %}
       ssl_ca_crt_file = {{ openstack_cacert }}