Cherry-pick #19531 to 7.x: Add docker logs support to the Elastic Log Driver

[fearful-symmetry]

Cherry-pick of PR #19531 to 7.x branch. Original message:

What does this PR do?

See #19371 and #13990

This PR adds support for the docker logs command to the Elastic Log Driver. This basically re-implements the "default" log driver, using Docker's own libraries, inside the Elastic Log Driver. In theory this should be a simple addition, as we're just gluing existing libraries on top on what we already have.

There's still some oddities going on here:

• We're getting interesting error messages if you run docker logs -f for an expended period of time without additional log lines: Error grabbing logs: error decoding log message: net/http: request canceled (Client.Timeout exceeded while reading body) This doesn't seem to be something in my library. Looks like it was due to this PR here: add a 10s timeout to the client object. docker/cli#1872

Why is it important?

This is a "must have" from the Cloud folks, and it's good to have in general. Also required for docker certification.

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
• I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc.

How to test this PR locally

1. build and install the plugin via mage buildAndInstall
2. Checkout the main readme in dockerlogbeat for an example of how to run the plugin against a container
3. Run the docker logs command against that container with various options, make sure everything works as expected.

[elasticmachine]

Pinging @elastic/integrations (Team:Integrations)

[elasticmachine]

💚 Build Succeeded

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Build stats

• Build Cause: [Pull request #19808 opened]

• Start Time: 2020-07-09T17:26:31.734+0000

• Duration: 31 min 28 sec

Test stats 🧪

Test	Results
Failed	0
Passed	3
Skipped	0
Total	3

Steps errors

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• Name: Report to Codecov

  • Description: curl -sSLo codecov https://codecov.io/bash for i in auditbeat filebeat heartbeat libbeat metricbeat packetbeat winlogbeat journalbeat do FILE="${i}/build/coverage/full.cov" if [ -f "${FILE}" ]; then bash codecov -f "${FILE}" fi done

  • Duration: 2 min 22 sec

  • Start Time: 2020-07-09T17:55:10.969+0000

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