Add docker repo key adding the docker repo

Change-Id: I752a1c3d746aec3fa417a416311f5d6a7730aee2
(cherry picked from commit 81d139027a0bd3dfce532a249a2fc18b26ab1c20)
diff --git a/ansible/roles/docker/tasks/debian.yml b/ansible/roles/docker/tasks/debian.yml
index cb080f9..93299d5 100644
--- a/ansible/roles/docker/tasks/debian.yml
+++ b/ansible/roles/docker/tasks/debian.yml
@@ -1,3 +1,7 @@
+- name: Trust docker apt key
+  apt_key:
+    data={{ lookup('file', 'docker_apt_key.gpg') }}
+
 - name: Debian add Docker repository and update apt cache
   apt_repository:
     repo: deb https://apt.dockerproject.org/repo ubuntu-{{ debian_version }} main