CI: Use Ubuntu Bionic in jobs

Many of the supporting infrastructure used to run Armada jobs, adopted
form OpenStack-Helm infra, no longer supports Ubuntu Xenial. This change
changes the default job distribution to Bionic in order to consume new
infrastructure code changes.

Change-Id: I3a2f1f95eae98cacc08641dc64ba7afbee628284
Signed-off-by: Drew Walters <andrew.walters@att.com>

.zuul.yaml

@@ -46,7 +46,7 @@
     name: armada-single-node
     nodes:
       - name: primary
-        label: ubuntu-xenial
+        label: ubuntu-bionic
 
 - job:
     name: armada-chart-build-gate

tools/gate/playbooks/airskiff-deploy.yaml

@@ -14,6 +14,16 @@
 
 - hosts: primary
   tasks:
+    # Stop systemd-resolved service before starting docker.
+    - name: stop systemd-resolved service
+      systemd:
+        state: stopped
+        enabled: no
+        masked: yes
+        daemon_reload: yes
+        name: systemd-resolved
+      become: yes
+
     - name: Clone Required Repositories
       shell: |
         export CLONE_ARMADA={{ CLONE_ARMADA }}