Expand kitchen-vcenter driver documentation

[tas50]

This is part of the large project to fully document all of the Test Kitchen drivers we ship in Chef Workstation. A skeleton driver has been created at https://kitchen.ci/docs/drivers/vcenter/. This provides an example only. We need to expand this to document the configuration options available.

Here is an example of how I've done this for the kitchen-digitalocean driver:

https://kitchen.ci/docs/drivers/digitalocean/

We briefly describe the driver and then include 3 sections

• Example kitchen.yml: Show a minimal example config
• Setting Driver Configuration: Explain how to set global vs. platform level driver config. This mostly just needs to get copied from digitalocean with the examples renamed
• Driver Configuration Options: This breaks down each of the configuration options available in this drive. Critical configs necessary to be successful like auth and image configuration options come first. After that just document them all.

The final step is to update the readme of the repo to point to these docs and include a note in the PR template and readme letting folks know to update these new centrally located docs.