Update metricbeat tests to use 7.4 version of the stack

[exekias]

For instance, dashboards tests depend on these containers. So dashboards created with > 7.3.0 wouldn't pass tests without this change

[odacremolbap]

looking good. Not sure if these points above might be missing, or part of a different set of issues:

• part of this issue - this was recently updated to use 7.3.2, I bet it would be best to have all of these pointing to 7.4.0. Not sure if the environment variables {ES/KIB/LS}_VERSION can be used https://github.com/elastic/beats/blob/master/testing/environments/latest.yml

• not part of this issue - obslethe metricbeat version for this test:

  beats/metricbeat/module/golang/_meta/Dockerfile

  Line 1 in 660daa1

  FROM docker.elastic.co/beats/metricbeat:6.5.4

• not part of this issue - if there is a web resource that returns the current released version of elastic stack (is there?) it would be nice to add it at this script block https://github.com/elastic/beats/blob/master/metricbeat/module/kubernetes/_meta/test/docs/README.md#create-elasticsearch--kibana-instances

Can you check if the first point at this list is something to tackle here?

[exekias]

👍 I have updated also the latest environment. I suggest we move forward with issues for the other points?