ci-multinode: Use Ark package repositories to install packages

Similar to e9130b9 but applied to
ci-multinode rather than ci-aio.

Previously we were using Test Pulp on SMS lab, but this is out of
action. Switching to Ark allows CI jobs to run on Leafcloud (or anywhere
with Internet access).

Author: markgoddard

etc/kayobe/environments/ci-multinode/stackhpc-ci.yml

@@ -10,7 +10,8 @@ kolla_docker_namespace: stackhpc-dev
 
 # Host and port of a package repository mirror.
 # Build and deploy the development Pulp service repositories.
-stackhpc_repo_mirror_url: "http://pulp-server.internal.sms-cloud:8080"
+# Use Ark's package repositories to install packages.
+stackhpc_repo_mirror_url: "{{ stackhpc_release_pulp_url }}"
 stackhpc_repo_mirror_username: "skc-ci-aio"
 stackhpc_repo_mirror_password: !vault |
   $ANSIBLE_VAULT;1.1;AES256