member_batch_update() might find a loadbalancer with
a pool that contains no members, but calling split(',')
will result in an existing member list of ['']. Force
it to an empty list if there are no members.
Closes-Bug: #1912779
Change-Id: Iec46c3e1ebef822d43964e13962153dc8760ee42
(cherry picked from commit 6e30b8552c)