(PUP-2506) Trivial Ruby bug in Puppet::Resource::Ral

Prior to this commit, a bug is triggered when the Puppet::Error string
is interpolated. The #type method was called recursively and failed with
an ArgumentError: wrong number of arguments (0 for 1).

This commit fixes the bug by changing which variable is interpolated in
the string.  It also adds a spec test for this case.
Merge pull request #2719 from razalas/issue/master/pup-2506-trivial-ruby-bug-in-puppet-resource-ral

(PUP-2506) Error when evaluating #type in Puppet::Error message interpolation for Puppet::Resource::Ral