'Calculate available space on the NFS share.
:param path: example pool/nfs'

def _get_capacity_info(self, path):

    (pool, fs) = self._get_share_datasets(path)
    url = ('storage/pools/%s/filesystems/%s' % (pool, self._escape_path(fs)))
    data = self.nef.get(url)
    total = utils.str2size(data['bytesAvailable'])
    allocated = utils.str2size(data['bytesUsed'])
    free = (total - allocated)
    return (total, free, allocated)
