Connect GDK and other containers to the host network in e2e tests

What does this MR do and why?

Connect GDK and other containers to the host network in e2e tests, as per the documentation on using services and docker run with docker-in-docker.

• Removes duplication in container networking
• Adds Blocking and NonBlocking scenarios to group rspec tags (similar to Review(Non)Blocking, but signup is enabled on GDK).

Implements #410246 (closed)

Tasks

• Test building the base image: https://gitlab.com/gitlab-org/gitlab/-/jobs/4510970072
• Consider any other changes that might on appear in master: !124143 (closed)
  • I believe the changes shouldn't affect master (or any other) pipelines. The smoke tests run automatically but they pass in this MR and should run the same in master pipelines.
  • Just in case, I'm testing a few changes in !124143 (closed)
    • Forced an update of the gem cache. No problems expected but it's easy to test.
      • Seems fine apart from a warning that was already present: https://gitlab.com/gitlab-org/gitlab/-/jobs/4518889573.
    • Enabled reporting. I don't expect any problems but there are changes to how we specify the tests to run in each job so I want to confirm the reporting matches.
      • Looks good: https://gitlab.com/gitlab-org/gitlab/-/jobs/4518597519
    • Include the nightly pipeline. The airgapped tests only run there and the runner changes in this MR could affect those.
      • Ran in https://gitlab.com/gitlab-org/gitlab/-/pipelines/907787654. Failures are as in #414247 (closed)

Test results

Known failures in master:

• #415672 (closed)
• #415621 (closed)

Reliable tests passed against GDK:

• https://gitlab.com/gitlab-org/gitlab/-/jobs/4502793946
• https://gitlab.com/gitlab-org/gitlab/-/jobs/4502793947
• https://gitlab.com/gitlab-org/gitlab/-/jobs/4502793948
• https://gitlab.com/gitlab-org/gitlab/-/jobs/4502793949

One test failed in https://gitlab.com/gitlab-org/gitlab/-/jobs/4502793945 (qa/specs/features/api/1_manage/rate_limits_spec.rb). This MR was intended to focus on runners so I'll investigate and fix that remaining test in a subsequent MR. Same for any failures in the non-blocking tests.

Failures in load balancer tests are a pre-existing issue: #415648 (closed)

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.