main: get FQDN from facts

`getHostName` only provide the node name which is different from FQDN
name. We should use the resolver to get the FQDN instead. However, since
this is already done by `facter`, we just use the value provided in the
retrieved facts.
Merge pull request #8 from vincentbernat/fix/get-fqdn-from-facts

main: get FQDN from facts