Automatically select a test host from inventory file

Let Tobiko IR plugin look for default host names in inventory
when no one is given and use any of below
- undercloud-0 (standard for tripleo multinode setup)
- tempest (standard for OpenStack upstream CI)
- primary (another standard name)

When any of above is found, just use localhost as before

Change-Id: Idadcc0b80e26c6c933cd75b1b90a7cc18fda94cb

roles/infrared.yaml

@@ -1,6 +1,20 @@
 ---
 
-- hosts: '{{ test_host }}'
+- hosts: 'localhost'
+  tasks:
+    - name: "select test host from inventory"
+      set_fact:
+        test_host: '{{ item }}'
+      when:
+        - test_host is not defined
+        - item in hostvars
+      loop:
+        - "undercloud-0"
+        - "tempest"
+        - "primary"
+
+
+- hosts: '{{ test_host | default("localhost") }}'
   gather_facts: yes
   any_errors_fatal: yes
   roles:

roles/plugin.spec

@@ -16,8 +16,6 @@ subparsers:
         options:
           host:
             type: Value
-            required: True
-            default: localhost
             help: Target host where test cases are deployed and executed
             ansible_variable: test_host