Detect openstack_release in kolla-ansible deploy-bifrost

This ensures that the default value of openstack_release - "auto" - is
handled correctly when deploying bifrost.

Change-Id: I71e6fc5a6b82dc5d6788bf093cd079c45d890ffd

ansible/bifrost.yml

 ---
+- name: Detect openstack_release variable
+  hosts: bifrost
+  gather_facts: false
+  tasks:
+    - name: Get current kolla-ansible version number
+      local_action: command python -c "import pbr.version; print(pbr.version.VersionInfo('kolla-ansible'))"
+      register: kolla_ansible_version
+      changed_when: false
+      when: openstack_release == "auto"
+
+    - name: Set openstack_release variable
+      set_fact:
+        openstack_release: "{{ kolla_ansible_version.stdout }}"
+      when: openstack_release == "auto"
+  tags: always
+
 - name: Apply role bifrost
   hosts: bifrost
   roles: