Unmask Docker service in ClearLinux (#4583)

The docker service provided by the containers-basic bundle is masked
in ClearLinux distribution. This is causing errors in the following
steps. This commit ensures that the unit is not masked.

roles/bootstrap-os/tasks/bootstrap-clearlinux.yml

@@ -9,6 +9,7 @@
 - name: Make sure docker service is enabled
   systemd:
     name: docker
+    masked: no
     enabled: yes
     daemon_reload: yes
     state: started