RUBY-1587 Properly handle error labels sent by server

Author: saghm

lib/mongo/error/operation_failure.rb

@@ -182,6 +182,16 @@ def initialize(message = nil, result = nil, options = {})
         @code = options[:code]
         @code_name = options[:code_name]
         super(message)
+
+        if result
+          err_doc = result.send(:first_document)
+
+          if err_doc && err_doc['errorLabels']
+            err_doc['errorLabels'].each do |label|
+              add_label(label)
+            end
+          end
+        end
       end
     end
   end

lib/mongo/operation/get_more/result.rb

@@ -52,7 +52,7 @@ def cursor_document
         end
 
         def first_document
-          @first_document ||= reply.documents[0]
+          @first_document ||= reply && reply.documents[0]
         end
       end
     end

spec/support/transactions/operation.rb

@@ -114,12 +114,12 @@ def execute(collection, session0, session1)
         {
           'errorCodeName' => err_doc['codeName'] || err_doc['writeConcernError']['codeName'],
           'errorContains' => e.message,
-          'errorLabels' => (e.instance_variable_get(:@labels) || []) + (err_doc['errorLabels'] || [])
+          'errorLabels' => e.instance_variable_get(:@labels)
         }
       rescue Mongo::Error => e
         {
           'errorContains' => e.message,
-          'errorLabels' => e.instance_variable_get(:@labels) || []
+          'errorLabels' => e.instance_variable_get(:@labels)
         }
       end