For Nova+Ironic deployments we could run the enable_ssh_admin Mistral
workflow directly and take advantage of the public key injection via
os-collect-config, but since the script seems to work for both
deployed-server and Nova/Ironic envs, we can just use it
unconditionally and keep the logic DRY.
Change-Id: I2bae54d282591abc8a014cdce805e90305a7a34d
Closes-Bug: #1735173