Migrate to new NBI charm, and change in NGUI charm

- Fixes bug 1365
- Changes in the installer:
    - use site_url config to expose both NBI and NG-UI
    - use resources for images
- Changes in the NBI: some minor fixes
- Changes in the NG-UI: follow the same pattern as in the new set of
charms

Change-Id: I6a11009ddf9cd22689602b2a53ecf67f376830cb
Signed-off-by: David Garcia <david.garcia@canonical.com>
diff --git a/installers/charm/nbi/src/pod_spec.py b/installers/charm/nbi/src/pod_spec.py
index 77fff3e..96518b9 100644
--- a/installers/charm/nbi/src/pod_spec.py
+++ b/installers/charm/nbi/src/pod_spec.py
@@ -270,7 +270,7 @@
 
     annotations = {
         "nginx.ingress.kubernetes.io/proxy-body-size": "{}".format(
-            max_file_size + "m" if max_file_size > 0 else max_file_size
+            str(max_file_size) + "m" if max_file_size > 0 else max_file_size
         ),
         "nginx.ingress.kubernetes.io/backend-protocol": "HTTPS",
     }