I tried again with agent-stream: released and image-stream: daily (with Juju 2.1.2 from the stable ppa) on a fresh controller and observed the same:

Attribute                     From        Value
agent-metadata-url            default     ""
agent-stream                  controller  released
agent-version                 model       2.1.2
apt-ftp-proxy                 default     ""
apt-http-proxy                default     ""
apt-https-proxy               default     ""
apt-mirror                    default     ""
automatically-retry-hooks     controller  false
default-series                controller  xenial
development                   default     false
disable-network-management    default     false
enable-os-refresh-update      controller  false
enable-os-upgrade             controller  false
external-network              default     ""
firewall-mode                 default     instance
ftp-proxy                     default     ""
http-proxy                    default     ""
https-proxy                   default     ""
ignore-machine-addresses      default     false
image-metadata-url            default     ""
image-stream                  controller  daily
logforward-enabled            default     false
logging-config                model       <root>=WARNING;unit=DEBUG
net-bond-reconfigure-delay    default     17
network                       model       86125222-dd54-4df2-9421-235456fab193
no-proxy                      default     ""
provisioner-harvest-mode      default     destroyed
proxy-ssh                     default     false
resource-tags                 model       {}
ssl-hostname-verification     default     true
storage-default-block-source  model       cinder
test-mode                     controller  true
transmit-vendor-metrics       controller  false
use-default-secgroup          controller  true
use-floating-ip               default     false


Model           Controller      Cloud/Region             Version
auto-osci-sv08  auto-osci-sv08  serverstack/serverstack  2.1.2

App     Version  Status   Scale  Charm   Store       Rev  OS      Notes
ubuntu           waiting    0/4  ubuntu  jujucharms   10  ubuntu

Unit      Workload  Agent       Machine  Public address  Ports  Message
ubuntu/0  waiting   allocating  0        172.17.108.10          waiting for machine
ubuntu/1  waiting   allocating  1        172.17.108.12          waiting for machine
ubuntu/2  waiting   allocating  2        172.17.108.14          waiting for machine
ubuntu/3  waiting   allocating  3        172.17.108.3           waiting for machine

Machine  State    DNS            Inst id                               Series  AZ
0        pending  172.17.108.10  a2e6d361-e72f-4b85-aa2d-6383ce3ab8a0  xenial  nova
1        pending  172.17.108.12  9614d394-58f7-49a7-9578-1267cc7aa902  xenial  nova
2        pending  172.17.108.14  cf6c3952-1f71-4e6b-991e-295ea5703931  xenial  nova
3        pending  172.17.108.3   4072c647-2c7b-4eba-b085-3d507662cd24  xenial  nova


(clients) jenkins@juju-10f68a-osci-13:~/tools/foo/charm-test-infra$ openstack server list | grep auto-osci-sv08
| 4072c647-2c7b-4eba-b085-3d507662cd24 | juju-902164-auto-osci-sv08-3 | ACTIVE | auto-osci_108_net=172.17.108.3          | ubuntu-released/ubuntu-xenial-16.04-amd64-server-20170330-disk1.img |
| cf6c3952-1f71-4e6b-991e-295ea5703931 | juju-902164-auto-osci-sv08-2 | ACTIVE | auto-osci_108_net=172.17.108.14         | ubuntu-released/ubuntu-xenial-16.04-amd64-server-20170330-disk1.img |
| 9614d394-58f7-49a7-9578-1267cc7aa902 | juju-902164-auto-osci-sv08-1 | ACTIVE | auto-osci_108_net=172.17.108.12         | ubuntu-released/ubuntu-xenial-16.04-amd64-server-20170330-disk1.img |
| a2e6d361-e72f-4b85-aa2d-6383ce3ab8a0 | juju-902164-auto-osci-sv08-0 | ACTIVE | auto-osci_108_net=172.17.108.10         | ubuntu-released/ubuntu-xenial-16.04-amd64-server-20170330-disk1.img |