Fix incorrect variable names in `forwarder.pp`
Fix incorrect variable names in `forwarder.pp`

Update variables to match parameters.
Not just a lint error, an actual bug!

Signed-off-by: Alexander Fisher <60c6d277a8bd81de7fdde19201bf9c58a3df08f4@linfratech.co.uk>

ralfbosz/puppet-splunk,dhoppe/puppet-splunk,ralfbosz/puppet-splunk