Zun: Add zun-cni-daemon to compute node

Zun has a new component "zun-cni-daemon" which should be
deployed in every compute nodes. It is basically an implementation
of CNI (Container Network Interface) that performs the neutron
port binding.

If users is using the capsule (pod) API, the recommended deployment
option is using "cri" as capsule driver. This is basically to use
a CRI runtime (i.e. CRI plugin for containerd) for supporting
capsules (pods). A CRI runtime needs a CNI plugin which is what
the "zun-cni-daemon" provides.

The configuration is based on the Zun installation guide [1].
It consits of the following steps:
* Configure the containerd daemon in the host. The "zun-compute"
  container will use grpc to communicate with this service.
* Install the "zun-cni" binary at host. The containerd process
  will invoke this binary to call the CNI plugin.
* Run a "zun-cni-daemon" container. The "zun-cni" binary will
  communicate with this container via HTTP.

Relevant patches:
Blueprint: https://blueprints.launchpad.net/zun/+spec/add-support-cri-runtime
Install guide: https://review.opendev.org/#/c/707948/
Devstack plugin: https://review.opendev.org/#/c/705338/
Kolla image: https://review.opendev.org/#/c/708273/

[1] https://docs.openstack.org/zun/latest/install/index.html

Depends-On: https://review.opendev.org/#/c/721044/
Change-Id: I9c361a99b355af27907cf80f5c88d97191193495