The tests might start running and attempting to do DNS resolutions
before minidns has come up, which can cause false positives and flaky
tests.
This patch makes the entrypoint wait until minidns has come up, to fix
the problem.
The integration tests depend on having a DNS server that resolves
"localhost", which is unfortunate but currently unavoidable given
glibc's limitations ($HOSTALIASES only works on DNS-level aliases, and
does not do lookups in /etc/hosts).
Even under docker, this makes the tests depend on the DNS server, and
whether it resolves localhost or not.
In order to make the docker tests more hermetic and isolated from the
environment, this patch introduces a docker entrypoint that, within the
container, will launch minidns and override /etc/resolv.conf to use it.
This guarantees that the tests will be able to resolve localhost, and
also avoid accidental reliance on external DNS zones.
