The SSH private key will normally be in $HOME/.ssh/id_rsa_tripleo
so if that key is present, then use it. This is a more reliable
location than "{{ playbook_dir }}/ssh_key", which will go away
with Mistral. This change is also backwards compatible as it
will fall back to using "{{ playbook_dir }}/ssh_key" in the case
that $HOME/.ssh/id_rsa_tripleo is missing. Covers one extra case
where CephAnsibleEnvironmentVariables/ANSIBLE_PRIVATE_KEY_FILE
might have been needed.
Also switches nodes_uuid_command to use ceph-ansible's ansible.cfg as
config-download may not always provide "{{ playbook_dir }}/ansible.cfg"
Change-Id: Ic7e20844877492d7c4b85f7579e90f6c9de355ec
Closes-Bug: #1868864
eaa13ee254