gnutls tests failing in an IPv6 environment

[gilles-peskine-arm]

When we upgraded Docker on the CI and had IPv6 enabled, this caused many tests involving GnuTLS to fail. (Despite those tests passing locally on developer machines with IPv6 enabled)

In the long term we'll want IPv6 to work but for the time being we don't mind continuing with what works, which is to disable IPv6.

This issue is considered resolved when the GnuTLS tests pass in a CI environment with IPv6 enabled. This may involve changes in the Groovy scripts, changes in all.sh, or constraints on the network setup.

[bensze01]

The problem appears to be that the IPv6 network appears as if it were enabled to GnuTLS, even though docker, in its default config (as is on the OpenCI) restricts its bridges to IPv4.

To enable the full support for IPv6 networking in docker, we have to follow one of the options in this official guide