Updating 'root_url' config option does not fully work

[Martin Kalcok]

When config option 'root_url' is updated, the charm will update only local config files. However the landscape server evaluates root url from multiple sources (in order):

- env variable "LANDSCAPE_ROOT_URL"
- database "landscape-standalone-main" in table "system_configuration", key "landscape.root_url"
- local service config file

I'd love to link launchpad server code for reference but I failed to find where it's publicly hosted. The logic I mentioned above is implemented in function 'get_root_url()' in file 'canonical/landscape/model/configuration.py'.