The go-ceph rbd package provides the GroupSnapGetInfo function, but it
may return ErrUnsupported when called. Returning this error after
advertising the support for VolumeGroupSnapshot seems ugly.
In order to advertise support for VolumeGroupSnapshot,
SupportsGroupSnapGetInfo() can be used, which detects the required C
function of librbd.
Signed-off-by: Niels de Vos <ndevos@ibm.com>
