Fix apt-get networking problem on MIPS

If you are building a chroot with Debian MIPS (sid, Aug 2016) or other non-primary architectures you can get a strange message during a chroot creating:

Err:1 http://httpredir.debian.org/debian sid InRelease
  Temporary failure resolving 'httpredir.debian.org'
Reading package lists... Done

It happens because IPv6 works bad or does not work on MIPS so just add a hook /var/cache/pbuilder/hooks/G90forceIPv4 with the following content:

#!/bin/sh
echo 'Acquire::ForceIPv4 "True";' > /etc/apt/apt.conf.d/80forceIPv4