virlog: determine the hostname on startup CVE-2018-6764

virlog: determine the hostname on startup CVE-2018-6764

At later point it might not be possible or even safe to use getaddrinfo(). It
can in turn result in a load of NSS module.

Notably, on a LXC container startup we may find ourselves with the guest
filesystem already having replaced the host one. Loading a NSS module
from the guest tree would allow a malicous guest to escape the
confinement of its container environment because libvirt will not yet
have locked it down.