After an unfortnate timed restart of the provisioner, a volume that got
cloned did not get a `rbdVolume.VolID` set. The `.VolID` is used as the
CSI Volume Handle, and is a required attribute.
The `rbdVolume` and `rbdSnapshot` structs have a `.ToCSI()` function
that can do the validation of required attributes. This is now added,
including unit-tests.
Signed-off-by: Niels de Vos <ndevos@ibm.com>
