network/dhclient-script: set FQDN

network/dhclient-script: set FQDN

When booting with nfsroot, dracut doesn't necessarily set the initial
hostname correctly.

According to dhcp-options(5), the name may or may not be qualified with
the local domain. It goes on to say "it is preferable to use the
domain-name option to specify the domain name".

So dhclient-script needs to be able to handle the cases: a) where
host-name is fully qualified and domain name is also specified; b)
where hostname is fully qualified and the domain is not separately
specified; c) where host-name is "short" and domain-name is also
specified; and d) do its best where host-name is short but domain-name
is not specified.

The dhclient-script in initramfs does not handle case "c", apparently
the preferred situation properly, setting hostname to "short".

https://bugzilla.redhat.com/show_bug.cgi?id=756347