* Support `distributionPolicy` when creating regional instance group managers.
* Better match the API structure of distributionPolicy.
* Switch to "distribution_policy_zones".
This approach lets us more simply allow a list of zones to use, while
providing a deprecation path for implementing the distribution policy
field more holistically, avoiding backwards-incompatible changes.
* fix typo
* use slice instead of Set for flattenDP
This reverts commit 8ab9d96d25 and revives
the original commit that adds t.Parallel to all acceptance tests. It
turns out test failures were unrelated to this change (rather, they were
related to quota issues).
This reverts commit 42de44592f. It appears
there might be thread-safety issues as panics have started occuring when
parallism is ramped up. Reverting for now while investigating.