Move 'tools/hostname.yml' to 'tools/fqdn.yml'

Now the playbook name is more relevant to what it does. You can also
specify the new hostname and domain using 'fqdn' variable in inventory,
which is less awkward than using the inventory hostnames directly.
Update CHANGELOG.rst
Merge pull request #52 from drybjed/update-fqdn

Update fqdn.yml playbook