Django's default site needs to be properly configured and returned

Checking projects/tasks.py's: get_base_url() during the last upgrade I noticed it has some problems:

196 """
197 Get the base URL for the site.
198 """
199 current_site = Site.objects.get_current()
200 return urlparse.urlunparse(("http", current_site.domain, "/", "", "", ""))

1. Django's default site is still example.com when we deploy Capomastro, we don't have a fixture for it and we possibly should ship saner defaults using the production/staging domains.

2. This get_base_url() should IMHO clear out the cache of site objects (Site.objects.clear_cache()) to force Django to query the current site for real otherwise it'll always return the old default example.com cached in the DB, right?

3. It should return HTTPS by default (and it should be safe enough as we have redirects and we always want HTTPS)

As a sidenote, I had to file a RT so IS would workaround these during the last upgrade, via https://rt.admin.canonical.com/Ticket/Display.html?id=81195