Replace acl_config with acl-config in docs.

Change-Id: I8f7c8b0800da37a7e9b97e75571a03ac14214374
Reviewed-on: https://review.openstack.org/23823
Reviewed-by: Jeremy Stanley <fungi@yuggoth.org>
Approved: Clark Boylan <clark.boylan@gmail.com>
Reviewed-by: Clark Boylan <clark.boylan@gmail.com>
Tested-by: Jenkins