Add the `vmware/scenario/vcenter_only` alias to be able to identify the
vmware test roles that can be tested with just on vcenter instance.
Also, add a check to be sure we don't try to attach ESXi hosts if none
has been defined.
* Adds a new vmware module to support getting the folders and their paths within a datacenter
* Add integration tests
* Bump version added
* Refactor integration test
* Improve grammar in docs