Previously the post-deploy.yml playbook was executed with become: true,
and the admin-openrc.sh file templated without an owner or mode
specified. This resulted in admin-openrc.sh being owned by root with 644
permissions.

This change creates the file without become: true, and explicitly sets
the owner to the user executing Ansible, and the mode to 600.

Co-Authored-By: Mark Goddard <mark@stackhpc.com>

Closes-Bug: #1891704

Change-Id: Iadf43383a7f2bf377d4666a55a38d92bd70711aa