Bug#793942: rootskel: Support `hostname -f` command when unavailable in dns

[Arthur Gautier <baloo@gandi.net>]

Package: rootskel
Severity: normal
Tags: d-i patch

Dear Maintainer,

When running d-i in a dhcp environment and when fqdn is only provided
with dhcp and not available dns, udhcpc will drop the domainname in
/etc/hosts like:
> 127.0.1.1 hostname.acme.com hostname

But `hostname -d` will never read this file because the nsswitch.conf is
incorrectly configured (will only query dns by default). A patch is
provided to fix this.

Thanks!

-- System Information:
Debian Release: stretch/sid
  APT prefers unstable
  APT policy: (500, 'unstable')
Architecture: amd64 (x86_64)

Kernel: Linux 4.0.0-1-amd64 (SMP w/4 CPU cores)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: sysvinit (via /sbin/init)

--- a/src/etc/nsswitch.conf
+++ b/src/etc/nsswitch.conf
@@ -1,3 +1,4 @@
 passwd: files
 group: files
 shadow: files
+hosts: files dns