Fix "Can't convert symbol into string" error

If aliases argument is set to "undef" in puppet, the puppet parser function is
not beeing passed 'nil' as I would have excepted. Instead its beeing passed a
symbol ':undef'. Therefore we need to check this as well.
Allow specifying what to use as "name" for the hostkey

Allow specifying what to use as "name" for the hostkey, in order to allow a
specific hostkey for multiple hosts (e.g. hosts that are beeing adressed via a
VIP)
release