rbd: Add support for wiping RBD volumes

rbd: Add support for wiping RBD volumes

When wiping the RBD image will be filled with zeros started
at offset 0 and until the end of the volume.

This will result in the RBD volume growing to it's full allocation
on the Ceph cluster. All data on the volume will be overwritten
however, making it unavailable.

It does NOT take any RBD snapshots into account. The original data
might still be in a snapshot of that RBD volume.

Signed-off-by: Wido den Hollander <wido@widodh.nl>