
This adds the possibility to retrieve prometheus or aetos endpoint information from keystone. Aetos is expected to have the endpoint registered (Aetos's devstack plugin already does this) and admins can register plain prometheus in Keystone with a simple command. Previous functionality with using /etc/openstack/prometheus.yaml or env variables is kept unchanged. Change-Id: I20eb5858244f1202ab8bc1fa26bb46b41d927ac0