fix: apply container name to elastic-agent Docker services

[mdelapenya]

What does this PR do?

This PR avoids overridding the container_name of the elastic-agent service in a Docker Compose file, which avoids not needed calculations.

Why is it important?

I found an error while running the tests against a local version of the stack, and after debugging, found that if the DEV_MODE is enabled (services are not destroyed) the local Docker daemon is not able to recreate the containers properly.

I've not found an open issue related to this in the Compose repo, but I upgraded my local Docker engine very recently.

$ docker --version
Docker version 20.10.7, build f0df350

$ docker-compose --version
Docker Compose version v2.0.0-beta.6

I could have downgraded my local version and have tested again, but I consider this change (delegating the container name to Docker) should cover this use case.

On the other hand, when running the tests in DEVELOPER_MODE=true, I noticed Docker is not able to recreate containers properly. To reproduce it:

1. Run TAGS="fleet_mode_agent && revoke-token && debian" TIMEOUT_FACTOR=5 LOG_LEVEL=TRACE DEVELOPER_MODE=true ELASTIC_APM_ACTIVE=false make -C e2e/_suites/fleet functional-test
2. Run same command again: TAGS="fleet_mode_agent && revoke-token && debian" TIMEOUT_FACTOR=5 LOG_LEVEL=TRACE DEVELOPER_MODE=true ELASTIC_APM_ACTIVE=false make -C e2e/_suites/fleet functional-test

Because the services are not stopped, the second execution should fail with:

could not run compose file: [/Users/mdelapenya/.op/compose/profiles/fleet/docker-compose.yml /Users/mdelapenya/.op/compose/services/elastic-agent/debian/docker-compose.yml] - Local Docker compose exited abnormally whilst running docker-compose: [up -d]. exit status 2

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 run the Unit tests (make unit-test), and they are passing locally
• I have run the End-2-End tests for the suite I'm working on, and they are passing locally
• I have noticed new Go dependencies (run make notice in the proper directory)

Author's Checklist

• [ ]

How to test this PR locally

Important: disable DEVELOPER_MODE!!!

TAGS="fleet_mode_agent && revoke-token"   TIMEOUT_FACTOR=5    LOG_LEVEL=TRACE    DEVELOPER_MODE=false    ELASTIC_APM_ACTIVE=false make -C e2e/_suites/fleet functional-test

Related issues

• Discovered while testing ci: beats PR testing seems to pull in incorrect docker images during test #1323

[elasticmachine]

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• Start Time: 2021-07-20T12:24:24.187+0000

• Duration: 36 min 53 sec

• Commit: 71cb5f1

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