Fix disk used visualization in system host overview dashboard

[exekias]

What does this PR do?

This change updates the Disk Used to honor default collecting period
for fsstat metricset (1m). Visualization sets the query to >=1m to
make sure we get a big enough bucket size when querying fsstat metrics.

Why is it important?

Without this change the host overview dashboard may or may not show the correct value for used disk.

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 added tests that prove my fix is effective or that my feature works

Related issues

• Related Disk Usage visualization always 0 #12435

[exekias]

I included CHANGEME_HOSTNAME var (7972737) as tests were failing. When we test this we need to make sure that link between overall System overview and Host specific overview works. That means, when in the main System overview dashboard, clicking in one of the hosts in the histogram view leads to the host overview dashboard filtered to that host.

[exekias]

I had a chat with @narph, this is a good workaround for most cases (people using defaults), but we are keeping #12435 open to see if we can find a solution that is good for any configured period.

[elasticmachine]

Pinging @elastic/integrations (Team:Integrations)

[exekias]

In order to test this we need to deploy Metricbeat with the system module enabled (it is by default), then:

• Go to the system overview dashboard, check that our host appears in the hosts list
• Check that clicking on it goes to the host overview dashboard
• Check that the disk usage graphs have data (before the change that was not always the case)