'Add a volume to a consistency group
:param volume_id the eseries volume id
:param cg_id: the eseries cg id
:param repo_percent: percentage capacity of the volume to use for
capacity of the copy-on-write repository'

def add_consistency_group_member(self, volume_id, cg_id, repo_percent=20.0):

    path = self.RESOURCE_PATHS.get('cgroup_members')
    data = {'volumeId': volume_id, 'repositoryPercent': repo_percent}
    return self._invoke('POST', path, data, **{'object-id': cg_id})
