Introduce concurreny testing for the VCH Management APIs

[zjs]

This issue tracks introducing concurrency testing for the existing VCH Management API functionality (create, list, inspect, and delete).

Suggested tests include:

• [ ] List VCHs while one is being created
• [ ] List VCHs while one is being deleted
• [ ] List VCHs while one is being updated in a way that would affect its list-level representation
• [ ] Attempt to create two VCHs at the same time within a single datacenter
• [ ] Attempt to create two VCHs at the same time in separate datacenters
• [ ] Inspect a VCH while it is being created
• [ ] Inspect a VCH while it is being deleted
• [ ] Inspect a VCH while it is being reconfigured
• [ ] Inspect a VCH while it is being upgraded
• [ ] Attempt to delete a VCH while it is already being deleted

Design and discussion is needed to determine where and how these tests should be implemented.

As a part of this work, the "Concurrency" portions of 23-02-VCH-List.md, 23-03-VCH-Create.md, 23-04-VCH-Inspect.md, and 23-05-VCH-Delete.md should be updated to document the implementation details of the tests (and moved to a more appropriate location, if applicable).

[andrewtchin]

Tests should reliably reproduce concurrency failures if they are found