Revert "conf: Remove volOptions for VIR_STORAGE_POOL_RBD"

Revert "conf: Remove volOptions for VIR_STORAGE_POOL_RBD"

This reverts commit 035db37394ad11a39d47f8bd2b6a8a2734283cbf

Even though we only allow using RBD with raw volumes,
removing the options and the default format causes our
parser not to fill out the volume format and the backend code
rejects creating a non-raw volume.

Re-introduce the volume options to fix volume creation while
erroring out on requests to use non-raw formats.

https://bugzilla.redhat.com/show_bug.cgi?id=1724065

Signed-off-by: Ján Tomko <jtomko@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>