In case cloning failed, Ceph Mgr returns an additional attribute in the
response. The "failed" attribute contains an errno (as string?!) and a
description. It is useful for applications using go-ceph to report the
error back to the user.
As the CloneStatus is on the same level as the CloneFailure object in
the response, keeping strictly to the CephFS Mgr API would break
compatibility. Instead, a new CloneStatus.GetFailure() method has been
introduced, returning a CloneFailure type (or nil) object with details
about the failure.
Signed-off-by: Niels de Vos <ndevos@redhat.com>