Allow overriding docker version in prepare-docker-dind

This change allows overriding of docker version to be installed
when calling prepare-docker-dind role.
It also enables downgrading, allowing the
given version to be taken into account. Previously
the specified version was completely ignored.

Change-Id: Iee3827564f130498e9fad69ddea55278346b7cfe
Issue-ID: OOM-1906
Signed-off-by: Michal Zegan <m.zegan@samsung.com>
diff --git a/ansible/test/roles/prepare-docker-dind/tasks/main.yml b/ansible/test/roles/prepare-docker-dind/tasks/main.yml
index 3e109e8..c0bf154 100644
--- a/ansible/test/roles/prepare-docker-dind/tasks/main.yml
+++ b/ansible/test/roles/prepare-docker-dind/tasks/main.yml
@@ -20,4 +20,5 @@
   package:
     name: "docker-ce-{{ docker_version }}"
     state: present
+    allow_downgrade: true
   notify: Restart docker