Add host inventory metrics to azure compute_vm metricset

[kaiyan-sheng]

What does this PR do?

This PR is to add proposed host common fields into compute metricset:

• host.id
• host.name
• host.cpu.pct
• host.network.in.bytes
• host.network.in.packets
• host.network.out.bytes
• host.network.out.packets
• host.disk.read.bytes
• host.disk.write.bytes

Why is it important?

This PR is a part of the inventory schema work.

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc.

How to test this PR locally

1. Start Metricbeat azure module: ./metricbeat modules enable azure
2. Edit modules.d/azure.yml to only include compute_vm metricset:

- module: azure
  metricsets:
    - compute_vm
  enabled: true
  period: 300s
  client_id: '123'
  client_secret: '123'
  tenant_id: '123'
  subscription_id: '123'
  refresh_list_interval: 600s

3. Change add_host_metadata processor config in metricbeat.yml file:

processors:
  - add_host_metadata:
      replace_fields: false

4. Start metricbeat
5. You should see metrics from compute_vm metricset and includes fields listed above.

[elasticmachine]

Pinging @elastic/integrations-platforms (Team:Platforms)

[elasticmachine]

💚 Build Succeeded

Expand to view the summary

Build stats

• Build Cause: [Pull request #20641 updated]

• Start Time: 2020-08-20T20:58:46.945+0000

• Duration: 50 min 34 sec

Test stats 🧪

Test	Results
Failed	0
Passed	874
Skipped	72
Total	946

[narph]

LGTM