ci: dockerLogs step

[v1v]

What does this PR do?

This step will allow us to fulfil the below cases:

Given a docker/docker-compose provisioned Docker containers
When all the Docker containers are started
Then show the last log lines of each container

Given a docker/docker-compose provisioned Docker containers
When tests failed
Then show the last log lines of each container
And show the status of the Docker containers

Why is it important?

Reuse the same step across different projects that are already using it.

Related issues

Caused by elastic/apm-agent-rum-js#806
Used by:

• ci: use dockerLogs step apm-integration-testing#848
• ci: dockerLogs step apm-agent-python#852

Tasks

• Add UTs
• Add ITs if possible

Tests

• Forcing a command failure with the flag failNever: true

• Success build

[apmmachine]

💚 Build Succeeded

Expand to view the summary

Build stats

• Build Cause: [Pull request #570 updated]

• Start Time: 2020-06-02T14:44:27.487+0000

• Duration: 6 min 59 sec

Test stats 🧪

Test	Results
Failed	0
Passed	577
Skipped	8
Total	585

[v1v]

This particular file was copied from https://github.com/elastic/apm-integration-testing/pull/848/files#diff-b9a5772126bdcf3f23e1ec67c1c88f55

I only added some header, fixed some shell-lint defects and added a minor condition regarding whether the docker-compose file exists.

[mdelapenya]

LGTM