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 branch/default in 22 minutes and 46 seconds
latest
Status Job ID Name Coverage
  Lint
passed #207666
flake8

00:00:09

 
  Test Heptapod
passed #207673
docker-fully-native-inside

00:18:01

passed #207674
docker-fully-native-remote-0

00:21:02

passed #207675
docker-fully-native-remote-1

00:20:26

passed #207667
docker-inside

00:19:56

passed #207670
docker-native-inside

00:18:00

passed #207671
docker-native-remote-0

00:21:09

passed #207672
docker-native-remote-1

00:22:36

passed #207668
docker-remote-0

00:19:38

passed #207669
docker-remote-1

00:22:17