In the VMware tests, we call the datastores `ds1` and `ds2`. The first
one is read-only, the second is read-write and can be used to deploy
VMs. The naming convention was not clear enough and source of a lot
confusion and mistake.
We now have two better names:
- ro_datastore, which is ... read-only
- rw_datastore, the one that we can use to deploy new VM.
Until now, the module was only able to interact with vcenter. This
commit adds the ability to directly target an ESXi without the
`esxi_hostname` parameter.
