virutil: Do not use g_get_host_name() to obtain hostname

virutil: Do not use g_get_host_name() to obtain hostname

The problem is that g_get_host_name() caches the hostname in a
thread local variable. Therefore, it doesn't reflect any
subsequent hostname changes. While this might be acceptable for
logs where the hostname is printed exactly once when the libvirtd
starts up, it is not optimal for virGetHostnameImpl() which is
what our public virConnectGetHostname() API calls. If the
hostname at the moment of the first API invocation happens to
start with "localhost" or contains a dot, then no further
hostname changes will ever be reflected.

This reverts 26d9748ff11, partially.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>