Monasca Agent Libvirt issues with unqualified hostname

[Mariusz Karpiarz]

In an environment where hypervisors are identified with their FQDNs:

```
$ openstack compute service list | grep compute-intel01
| 34 | nova-compute | compute-intel01.novalocal | nova | enabled | up | 2020-09-03T09:38:23.000000 |
```
and with monasca-agent-collector's config coming from https://opendev.org/openstack/kolla-ansible/blame/commit/295f8d1b43cf2003f66634389fc0615609ee0f86/ansible/roles/monasca/templates/monasca-agent-collector/agent-collector.yml.j2, Monasca Agent is unable to find the `nova-compute` service on the hypervisor and ignores all the instances running on it:

```
[centos@compute-intel01 ~]$ sudo grep hostname /etc/kolla/monasca-agent-collector/agent-collector.yml
  hostname: compute-intel01
[centos@compute-intel01 ~]$ sudo cat /var/lib/docker/volumes/kolla_logs/_data/monasca/agent-collector.log
...
2020-09-03 09:17:16 UTC | WARNING | collector | monasca_agent.collector.checks.check.libvirt(libvirt.py:160) | No 'nova-compute' service found on host: compute-intel01
2020-09-03 09:17:16 UTC | ERROR | collector | monasca_agent.collector.checks.check.libvirt(libvirt.py:822) | instance-0000010c is not known to nova after instance cache update -- skipping this ghost VM.
2020-09-03 09:17:16 UTC | ERROR | collector | monasca_agent.collector.checks.check.libvirt(libvirt.py:822) | instance-000000ef is not known to nova after instance cache update -- skipping this ghost VM.
...
```
The above results in the list of instances for this host being empty and no instance-related metrics coming from the Libvirt plugin.

Removing the "hostname" config parameter fixes the problem:

```
[centos@compute-intel01 ~]$ sudo grep hostname /etc/kolla/monasca-agent-collector/agent-collector.yml
  #hostname: compute-intel01
[centos@compute-intel01 ~]$ sudo cat /var/lib/docker/volumes/kolla_logs/_data/monasca/agent-collector.log
...
2020-09-03 09:18:53 UTC | INFO | collector | monasca_agent.collector.checks.check.libvirt(libvirt.py:154) | Found 'nova-compute' registered with host: compute-intel01.novalocal
2020-09-03 09:18:54 UTC | INFO | collector | monasca_agent.collector.checks.collector(collector.py:99) | Finished run #1. Collection time: 1.26s.
...
```
This is because the Agent cannot match unqualified "hostname" parameter against the fully-qualified hypervisor name:
https://opendev.org/openstack/monasca-agent/src/commit/e021416e600f81d5ed544b1c66675719c3a896b6/monasca_agent/collector/checks_d/libvirt.py#L142-L163

The Agent can work out the hostname of the node it's running on automatically (using `hostname -f`) but the config parameter takes precedence:
https://opendev.org/openstack/monasca-agent/src/commit/e021416e600f81d5ed544b1c66675719c3a896b6/monasca_agent/common/util.py#L395-L404

Therefore I suggest we either remove the "hostname" parameter entirely or use `ansible_fqdn` instead.

[Tom Fifield (fifieldt)]

Hi Mariusz, are you still interested in working on this?