Revamp registry test

[apostasie]

The fundamental motivation for this is to fix #3044

Furthermore, before embarking on revamping login code to fix everything in #3072 we do need a clean working ready-to-go test tooling and environment (specifically fix #3071).

This PR does revamp testregistry, testca and adds a couple of files.

In a shell:

• testca now allows additional names
• portlock allows for "locking" a port (or finding a free one), that is not racy and safe to use with parallel across distinct invocations. This allows tests to not have to specify an explicit port anymore (if they don't want a specific one), which in turn allow for parralelization without risks of conflicts
• testregistry and login_linux_test have been largely rewritten and fix:
  • guarantee that cleanups are always done
  • add support for Basic Authentication
  • prevent cross registry pollution by using distinct credentials per registry
  • prevent credential pollution between tests by privatizing .docker/config.json
  • reduce duplication in testregistry
  • better host toml coverage for variants (w/o ports)
  • Auth server can now serve on http or https
  • parallelize as much as feasible
  • adding a larger variety of tests

Pending green CI, I would suggest we merge this ASAP so that further test cleanup can happen (and more parallelization) and actual work can begin on cleaning-up login

[apostasie]

CI is green

@AkihiroSuda and team PTAL at your convenience.

[apostasie]

Apologies for the re-push. Did mistakenly commit files from another PR.

[apostasie]

@AkihiroSuda if this looks fine to you folks, I would love to see this merged in as I have more CI and tests changes that would benefit from it.

I believe the windows failure is a fluke, so, if you can poke it that would be lovely.