allow naginator parameters to be forced absent #6266

http://projects.puppetlabs.com/issues/6266

This needs to be tested properly, but so far it doesn't break any of the
obvious spec files.

    rake spec SPEC=$(find spec | egrep 'nagios|naginator')
add new spec test for nagios_host

Based on spec/unit/provider/ssh_authorized_key/parsed_spec.rb