Upload arm64 images to linaro-london cloud

We have enabled this cloud region on our launchers but they cannot
launch images because the images are not being uploaded there yet.
Configure nb03 to upload to the cn1 and london arm clouds.

Change-Id: I85d1a002c6e0d9287e36fe3c04c982a25087ea70

nodepool/nb03.openstack.org.yaml

@@ -18,7 +18,7 @@ providers:
     region-name: 'RegionOne'
     cloud: linaro
     rate: 0.25
-    diskimages:
+    diskimages: &provider_diskimages
       - name: ubuntu-xenial-arm64
         pause: false
         config-drive: true
@@ -44,6 +44,12 @@ providers:
           hw_disk_bus: scsi
           hw_scsi_model: virtio-scsi
 
+  - name: linaro-london
+    region-name: 'London'
+    cloud: linaro-london
+    rate: 0.25
+    diskimages: *provider_diskimages
+
 diskimages:
   - name: ubuntu-xenial-arm64
     elements: