Remove custom FQDN from .travis.yml

It seems that using 'localhost.localdomain' on Travis should suffice for
role testing.
Add a symlink for preseed templates on Travis CI

At the moment there is no preseed configuration specifically for
Precise, which makes the test fail on Travis CI, which uses Ubuntu
Precise. Wheezy configuration files should work fine in this context,
and for other distributions like Jessie, we might use similar solution
if preseed files work with their installers.