fetchstatus.py was a Django management command, and is now
a standalone script. This way we avoid doing Django housekeeping
every time it runs (every 10 seconds). It still needs to access
the ALLOWED_HOSTS setting, to make the HTTP request with
a correct Host header.
Fixes: #1071
Commit 8fed685f12 added a HEALTHCHECK
instruction in the Dockerfile. The healthcheck script calls http://localhost:8000/api/v3/status/, which fails if localhost is not in ALLOWED_HOSTS.
With this change, the healthcheck script is now a Django management
command. It reads Django's ALLOWED_HOSTS setting, grabs the first
element, and uses it in the "Host:" HTTP header when making a HTTP
request.
cc: #1051
