Make rule parse failures show useful warnings

By default the test failure output when a rule is unparseable is just
`undefined method '[]' for nil:NilClass`, which does not meaningfully
indicate that an error has happened in parsing, or which error.  This
makes any current or future warning from the parser appear in test
failure output.

Author: greatflyingsteve

spec/unit/puppet/provider/ip6tables_spec.rb

@@ -101,13 +101,15 @@ def stub_iptables
         # If this option is enabled, make sure the parameters exactly match
         if data[:compare_all]
           it 'the parameter hash keys should be the same as returned by rules_to_hash' do
+            expect(provider6).not_to receive(:warning)
             expect(resource.keys).to match_array(data[:params].keys)
           end
         end
 
         # Iterate across each parameter, creating an example for comparison
         data[:params].each do |param_name, param_value|
           it "the parameter '#{param_name}' should match #{param_value.inspect}" do
+            expect(provider6).not_to receive(:warning)
             if param_value == true
               expect(resource[param_name]).to be_truthy
             else

spec/unit/puppet/provider/iptables_spec.rb

@@ -219,13 +219,15 @@
         # If this option is enabled, make sure the parameters exactly match
         if data[:compare_all]
           it 'the parameter hash keys should be the same as returned by rules_to_hash' do
+            expect(provider).not_to receive(:warning)
             expect(resource.keys).to match_array(data[:params].keys)
           end
         end
 
         # Iterate across each parameter, creating an example for comparison
         data[:params].each do |param_name, param_value|
           it "the parameter '#{param_name}' should match #{param_value.inspect}" do
+            expect(provider).not_to receive(:warning)
             # booleans get cludged to string "true"
             if param_value == true
               expect(resource[param_name]).to be_truthy