Fix nodes accessor

Author: cjmartian

Diff for: lib/octofacts/backends/index.rb

@@ -45,7 +45,7 @@ def select(conditions)
           add_fact_to_index(key) unless indexed_fact?(key)
           matching_nodes = index[key][value.to_s]
           raise Octofacts::Errors::NoFactsError if matching_nodes.nil?
-          self.nodes = nodes & matching_nodes
+          @nodes = nodes & matching_nodes
         end
 
         self
@@ -62,7 +62,7 @@ def reject(conditions)
           end
         end
 
-        self.nodes = matching_nodes
+        @nodes = matching_nodes
         self
       end
 
@@ -72,7 +72,7 @@ def prefer(conditions)
           add_fact_to_index(key) unless indexed_fact?(key)
           matching_nodes = index[key][value.to_s]
           unless matching_nodes.nil?
-            self.nodes = (matching_nodes.to_set + nodes.to_set).to_a
+            @nodes = (matching_nodes.to_set + nodes.to_set).to_a
           end
         end