local.defaults: Setup Gluster cluster on CentOS 8 platform

Unavailability of complete gluster-ansible packages and limitation[1]
to use latest ansible versions forces us to setup GlusterFS cluster
using older versions on CentOS 8 platform.

[1] gluster/gluster-ansible-infra#135

Signed-off-by: Anoop C S <anoopcs@cryptolab.net>

vagrant/roles/local.defaults/vars/main.yml

@@ -100,6 +100,7 @@ environments:
         networks:
           private: 200
         groups: [admin]
+        os: centos8
 
       client:
         networks:
@@ -115,6 +116,7 @@ environments:
         ctdb:
           public: 10
         groups: [cluster]
+        os: centos8
 
   xfs:
     cpus: 2