Investigate vagrant-lxc for our build system

The vagrant-lxc provider will likely offer better performance than a true VM-based provider, like VirtualBox or libvirt (#6354 (closed)), especially if makes it possible to avoid nested VMs, which will be the case for our build server.

However, LXC may not separate from the host as effectively as a true VM, thus possibly bringing back the old issues of having input devices disconnect, or even the X server restarting, etc. Even if there would be such problems it could be nice to have as an optional provider to be used only on systems where that won’t matter, like our build server (probably). That’s only relevant, though, if it noticeably increases performance.

A plus is that there’s already an ITP for it.

Related issues

• Is duplicate of #10232 (closed)

Original created by @anonym on 6787 (Redmine)