This is a followup to running tests in serial in CI.
Since the API package cannot import anything outside of api/,
copy the ci.Parallel function into api/internal/testutil, and
have api tests use that.
* Divest api/ package of deps elsewhere in the nomad repo.
This will allow making api/ a module without then pulling in the
external repo, leading to a package name conflict.
This required some migration of tests to an apitests/ folder (can be
moved anywhere as it has no deps on it). It also required some
duplication of code, notably some test helpers from api/ -> apitests/
and part (but not all) of testutil/ -> api/testutil/.
Once there's more separation and an e.g. sdk/ folder those can be
removed in favor of a dep on the sdk/ folder, provided the sdk/ folder
doesn't depend on api/ or /.
* Also remove consul dep from api/ package
* Fix stupid linters
* Some restructuring
Embed pointer conversion functions in the API package to avoid
unnecessary package dependency. `helper` package imports more
dependencies relevant for internal use (e.g. `hcl`).
