- remove the unsupported alias
- refactoring
- move the hosts outside of the cluster to avoid any conflict with DRS
- import the `prepare_vmware_tests` role
- does not work with govcsim
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.