The Manager.MakeVolumeGroupID() function can be used to build a CSI
VolumeGroupID from the backend (pool and name of the RBD-group). This
will be used when checking if an RBD-image belongs to a group already.
It is also possible to resolve the VolumeGroup by passing the
VolumeGroupID to the existing Manager.GetVolumeGroupByID() function.
Signed-off-by: Niels de Vos <ndevos@ibm.com>
