creating lxc containers on arm devices fails

I am setting up openstack-ansible on a heterogeneous cluster consisting of an x86 control node and arm compute nodes. For services (e.g. a repo service) to also run on the arm nodes containers need to be created on the arm nodes.

Encountered failure:
Container creation of openstack-ansible fails with the following error during TASK [lxc_hosts : Create base container]:
fatal: [odroid]: FAILED! => {"changed": false, "command": "/usr/bin/lxc-create --name LXC_NAME --quiet --template download --bdev dir -- --dist ubuntu --release xenial --arch --force-cache --server images.linuxcontainers.org --variant default \n --keyserver hkp://p80.pool.sks-keyservers.net:80", "err": "", "failed": true, "msg": "Failed executing lxc-create.", "rc": 1}

Reason for failure:
lxc-create cannot resolve the template argument arch=''.

Suggested fix:
Add an architecture mapping for arm:
 lxc_architecture_mapping:
      x86_64: amd64
      ppc64le: ppc64el
      armv7l: armhf

This mapping update needs (at least) to be applied to:
- ansible/roles/lxc_hosts/defaults/main.yml
- ansible/roles/lxc_container_create/defaults/main.yml

Please note that the above list may not be complete. I chose to redefine the mentioned variable in user_variables which allowed successful container creation on the arm host.