Reverse calls: explicit IP addresses

It can happen that WSGIServer (itself based on socketserver.BaseServer)
binds by default using IPv4 while the `localhost` default call address
that will be stored on the Rails side for reverse calls will resolve to
`::1`. Since some of the contexts for these tests only have IPv4 (Docker
containters), we're binding explicitely to the all IPv4 addresses 0.0.0.0

On many Linux systems, the kernel is configured so that :: serves all
IPv6 and IPv4 address (through representation of the IPv4 address
space in IPv6). We'' switch to that if we turn out to need IPv6 and it works
in our Docker CI contexts. For now, let's spare us another round of testing.
10 jobs for topic/default/gitlab-13.12 in 10 seconds (queued for 1 second)
Status Job ID Name Coverage
  Lint
passed #207646
flake8

00:00:10

 
  Test Heptapod
manual #207653
allowed to fail manual
docker-fully-native-inside
manual #207654
allowed to fail manual
docker-fully-native-remote-0
manual #207655
allowed to fail manual
docker-fully-native-remote-1
manual #207647
manual
docker-inside
manual #207650
manual
docker-native-inside
manual #207651
manual
docker-native-remote-0
manual #207652
manual
docker-native-remote-1
manual #207648
manual
docker-remote-0
manual #207649
manual
docker-remote-1