Remove hardcoded region and availability zone

This can be set via envvar, no point in hardcoding, which btw
can lead to issues on users with accounts on regions different
to region-b

roles/provision_infra_servers/tasks/main.yml

@@ -4,8 +4,6 @@
     state: present
     cloud: "{{os_client_config_cloud}}"
     name: "{{ item.name }}.{{ domainname }}"
-    region_name: region-b.geo-1
-    availability_zone: az2
     image: "{{ item.image }}"
     key_name: "{{ key_name }}"
     timeout: 200