Zun: add CNI loopback binary to the image

Change-Id: I2d6165c4b7e934c3e6ad32b3de1060d07b792463
Needed-By: https://review.opendev.org/#/c/708213/

docker/zun/zun-cni-daemon/Dockerfile.j2

@@ -36,5 +36,9 @@ COPY zun_sudoers /etc/sudoers.d/kolla_zun_sudoers
 RUN chmod 750 /etc/sudoers.d \
     && chmod 640 /etc/sudoers.d/kolla_zun_sudoers
 
+RUN curl -sSL -o /tmp/cni-plugins-v0.7.1.tgz https://github.com/containernetworking/plugins/releases/download/v0.7.1/cni-plugins-amd64-v0.7.1.tgz \
+    && tar -C /opt -xzvf /tmp/cni-plugins-v0.7.1.tgz ./loopback \
+    && rm -f /tmp/cni-plugins-v0.7.1.tgz
+
 {% block zun_cni_daemon_footer %}{% endblock %}
 {% block footer %}{% endblock %}