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.
