MNAIO: Add supported distro check and remove trusty support

Ubuntu Trusty is too old to support much of what this tooling does,
so we remove support for it and add a task to verify that a supported
distribution version is being used.

Change-Id: I0247be130dd4adf1d1d50518e6ec5c617a3a8f7c

multi-node-aio/playbooks/setup-host.yml

@@ -20,6 +20,16 @@
   tags:
     - setup-host
   tasks:
+    - name: Check for a supported Operating System
+      assert:
+        that:
+          - (ansible_distribution == 'Ubuntu' and ansible_distribution_release == 'xenial') or
+            (ansible_distribution == 'Ubuntu' and ansible_distribution_release == 'bionic')
+        msg: >-
+          The only supported host platforms for this tooling are Ubuntu 16.04 LTS (Xenial)
+          and Ubuntu 18.04 LTS (Bionic). Patches to add support for other distributions are
+          most welcome.
+
     - name: Gather variables for each operating system
       include_vars: "{{ item }}"
       with_first_found:

multi-node-aio/playbooks/vars/ubuntu.yml

@@ -17,10 +17,6 @@ mnaio_host_required_distro_packages:
   - ubuntu-cloud-keyring
 
 mnaio_host_package_repos:
-  - repo: "deb http://ubuntu-cloud.archive.canonical.com/ubuntu {{ ansible_lsb.codename }}-updates/mitaka main"
-    state: present
-    filename: "uca"
-    condition: "{{ ansible_lsb.codename == 'trusty' }}"
   - repo: "deb http://ubuntu-cloud.archive.canonical.com/ubuntu {{ ansible_lsb.codename }}-updates/queens main"
     state: present
     filename: "uca"