Stop systemd-resolved to fix DNS configuration

Docker uses DNS configuration from systemd-resolved,
when its running [1], stop it before starting docker
to use /etc/resolv.conf instead.

The issue has been introduced with Ubuntu Bionic,
because it brings systemd-resolved service for DNS
management.

[1] https://github.com/moby/moby/commit
      /e353e7e3f0ce8eceeff657393cba2876375403fa

Change-Id: I8cabbc6b49383e3ac4e5596e574ffbe59ec1ee67

tools/gate/playbooks/airskiff-deploy-gate.yaml

@@ -14,6 +14,16 @@
 
 - hosts: ubuntu-bionic
   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: Install required packages
       shell: |
         ./tools/deployment/airskiff/developer/000-install-packages.sh