ceph-windows: Use vstart cluster for Ceph Windows tests

ceph-windows: Use vstart cluster for Ceph Windows tests

Previously, we spawned a minimal cluster with `cephadm` just to have
a Ceph API available (without any OSDs configured).

New Ceph Windows tests will be available that require actual Ceph
store, so a fully functional Ceph cluster is needed.

The entire ceph-windows testing is done with libvirt VMs now.
This way, we avoid accidentally tainting the CI machines after
each job run.

Building and running Ceph vstart doesn't drastically impact the job
running times, since the CI machines have a lot of CPU cores available.

Signed-off-by: Ionut Balutoiu <ibalutoiu@cloudbasesolutions.com>