Automate installation of newly distributed exporters

[dann1]

With OpenNebula/one#7508 we are now distributing new exporters

root@PC04:~# apt search opennebula-prometheus
Sorting... Done
Full Text Search... Done
opennebula-prometheus/stable,now 7.2.1-1 amd64 [installed]
  OpenNebula Prometheus and Grafana (Enterprise Edition)

opennebula-prometheus-kvm/stable,now 7.2.1-1 amd64 [installed]
  OpenNebula KVM Exporters (Enterprise Edition)

opennebula-prometheus-lvm/stable 7.2.1-1 amd64
  OpenNebula Prometheus LVM Exporter (Enterprise Edition)

opennebula-prometheus-mysql/stable 7.2.1-1 amd64
  OpenNebula Prometheus MySQL Exporter (Enterprise Edition)

opennebula-prometheus-ovs/stable 7.2.1-1 amd64
  OpenNebula Prometheus Open vSwitch Exporter (Enterprise Edition)

opennebula-prometheus-smartctl/stable 7.2.1-1 amd64
  OpenNebula Prometheus SMART Exporter (Enterprise Edition)

We would need to

• install them as well when suitable (if using OVS, LVM)
  • mysql in the frontend, the rest in the nodes
  • perhaps is simpler to declare extra exporters in the node where they are needed in the inventory
• provide the same treatment with systemd overrides F OpenNebula/engineering#751: Use drop-ins to configure oneprometheus systemd units #187

As of now there are two bugs packaging wise

• The metadata in the ovs exporter is strict as far as package name goes. Can break both deb and rhel existing ovs installations
• The mysql exporter fails to start because it requires a credentials file that is not automatically generated
  • This is being handled via packaging, based on /etc/one/oned.conf DB credentials