'Creates a group_snapshot.
:param context: the context of the caller.
:param group_snapshot: the GroupSnapshot object to be created.
:param snapshots: a list of Snapshot objects in the group_snapshot.
:returns: model_update, snapshots_model_update'

def create_group_snapshot(self, context, group_snapshot, snapshots):

    if (not utils.is_group_a_cg_snapshot_type(group_snapshot)):
        raise NotImplementedError()
    cg_name = ('cg_snap-' + group_snapshot.id)
    self._helpers.create_fc_consistgrp(cg_name)
    timeout = self.configuration.storwize_svc_flashcopy_timeout
    (model_update, snapshots_model) = self._helpers.run_consistgrp_snapshots(cg_name, snapshots, self._state, self.configuration, timeout)
    return (model_update, snapshots_model)
