feat: support for running feature files

[mdelapenya]

What does this PR do?

This PR adds support for running feature files, without changing how the TAGS filters are used.

• extracts common logic to run the tests to a common-test.mk file.
• create a Makefile for each test suite, providing each test suite the run tests command, like in a build system for a multi-module project. This new file imports the new common file.
• adds support to filter the test runner by feature file, so that the run tests command is able to select one or more feature files.

We are also documenting how the CI is spreading the scenarios in the workers, using the .e2e-tests.yaml descriptor.

Finally, it improves the docs related the variables that affect the build, including TAGS and FEATURES.

Why is it important?

This PR is the first step to simplify how the scenarios are spread in the parallel workers: nowadays it's using TAGS, but and the end of the day we are using feature files (using the tag for the entire feature file).

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)

How to test this PR locally

Default execution:
It will run all feature files, filtered by the backend_processes && debian && install tags.

TAGS="backend_processes && debian && install" TIMEOUT_FACTOR=3 LOG_LEVEL=TRACE BEATS_USE_CI_SNAPSHOT=true  DEVELOPER_MODE=true make -C e2e         functional-test

Running with features:
It will run the fleet_mode_agent.feature file, filtering by the backend_processes && debian && install tags.

FEATURES="fleet_mode_agent.feature" TAGS="backend_processes && debian && install" TIMEOUT_FACTOR=3 LOG_LEVEL=TRACE BEATS_USE_CI_SNAPSHOT=true  DEVELOPER_MODE=true make -C e2e functional-test

Related issues

• Relates Spread tests on CI by feature file instead of by tags #1191
• Relates Refactor Gherkin tag names #373 (as after this PR we will be able to filter by feature file instead of the parent tag, being possible to refactor child tags without changing execution)

Follow-ups

We need to update the e2e YAML descriptor to match this new features approach, updating the Jenkinsfile to spread feature files into the parallel execution. Besides that, we could generate the descriptor on the fly, based on the existing feature files.

[elasticmachine]

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Build stats

• Build Cause: Pull request #1193 updated

• Start Time: 2021-05-25T21:42:19.810+0000

• Duration: 21 min 23 sec

• Commit: cd516bf

Test stats 🧪

Test	Results
Failed	0
Passed	160
Skipped	0
Total	160

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Test stats 🧪

Test	Results
Failed	0
Passed	160
Skipped	0
Total	160

[mdelapenya]

jenkins run the tests please