Set undercloud hostname from ansible variables

This sets the undercloud hostname from ansible variables instead of
having to call hostnamectl. This also sets a domain to the hostname if
needed.

The hostname is set with one of the following cases, in this order of
precedence

* When we have undercloud_cloud_domain defined, we use that for the FQDN
* When we have an FQDN we use that.
* If not, we default to <hostname>.tripleodomain.example.com

Note that these are only used if undercloud_undercloud_hostname wasn't
provided.

Depends-On: I7705744cab62f432e2e09bf1ee88bba809609cda 
Change-Id: I649d6cb87458f2bc9623c84830a45bdcf54432d4
Closes-Bug: #1801769

roles/undercloud-setup/tasks/hostname.yml

@@ -21,12 +21,29 @@
   when:
     - not release in ['newton','ocata','pike','queens']
     - containerized_undercloud|bool
+    - undercloud_undercloud_hostname is not defined
   block:
-    - name: Get the hostname info
-      command: hostnamectl --static
-      register: hostnamectl_result
+    - name: set fact for undercloud_fqdn override when undercloud_cloud_domain was provided
+      set_fact:
+        undercloud_fqdn: "{{ ansible_hostname }}.{{ undercloud_cloud_domain }}"
+      when:
+      - undercloud_cloud_domain is defined
+
+    - name: set fact for undercloud_fqdn override when we have a domain
+      set_fact:
+        undercloud_fqdn: "{{ ansible_fqdn }}"
+      when:
+      - ansible_domain|default("") != ""
+      - undercloud_cloud_domain is not defined
+
+    - name: set fact for undercloud_fqdn override when we don't have a domain
+      set_fact:
+        undercloud_fqdn: "{{ ansible_hostname }}.tripleodomain.example.com"
+      when:
+      - ansible_domain|default("") == ""
+      - undercloud_cloud_domain is not defined
 
     - name: Set fact for undercloud_hostname override
       set_fact:
         cacheable: true
-        undercloud_undercloud_hostname: "{{ hostnamectl_result.stdout }}"
+        undercloud_undercloud_hostname: "{{ undercloud_fqdn }}"