MAGETWO-66656: Fix retrieval of old value in config import

Author: shiftedreality

app/code/Magento/Config/etc/di.xml

@@ -86,6 +86,19 @@
             <argument name="serializer" xsi:type="object">Magento\Framework\Serialize\Serializer\Serialize</argument>
         </arguments>
     </type>
+    <virtualType name="systemSnapshot" type="Magento\Config\App\Config\Type\System">
+        <arguments>
+            <argument name="source" xsi:type="object">systemConfigSnapshotSourceAggregated</argument>
+            <argument name="configType" xsi:type="string">system_snapshot</argument>
+        </arguments>
+    </virtualType>
+    <virtualType name="configSnapshot" type="Magento\Framework\App\Config">
+        <arguments>
+            <argument name="types" xsi:type="array">
+                <item name="system" xsi:type="object">systemSnapshot</item>
+            </argument>
+        </arguments>
+    </virtualType>
     <virtualType name="modulesDataProviderProxy" type="Magento\Framework\App\Config\InitialConfigSource\Proxy">
         <arguments>
             <argument name="instanceName" xsi:type="string">modulesDataProvider</argument>
@@ -124,6 +137,24 @@
         </arguments>
     </virtualType>
     <virtualType name="systemConfigSourceAggregated" type="Magento\Framework\App\Config\ConfigSourceAggregated">
+        <arguments>
+            <argument name="sources" xsi:type="array">
+                <item name="modular" xsi:type="array">
+                    <item name="source" xsi:type="object">Magento\Config\App\Config\Source\ModularConfigSource</item>
+                    <item name="sortOrder" xsi:type="string">10</item>
+                </item>
+                <item name="dynamic" xsi:type="array">
+                    <item name="source" xsi:type="object">Magento\Config\App\Config\Source\RuntimeConfigSource</item>
+                    <item name="sortOrder" xsi:type="string">100</item>
+                </item>
+                <item name="initial" xsi:type="array">
+                    <item name="source" xsi:type="object">systemConfigInitialDataProvider</item>
+                    <item name="sortOrder" xsi:type="string">1000</item>
+                </item>
+            </argument>
+        </arguments>
+    </virtualType>
+    <virtualType name="systemConfigSnapshotSourceAggregated" type="Magento\Framework\App\Config\ConfigSourceAggregated">
         <arguments>
             <argument name="sources" xsi:type="array">
                 <item name="modular" xsi:type="array">
@@ -248,4 +279,9 @@
             </argument>
         </arguments>
     </type>
+    <type name="Magento\Framework\App\Config\Value">
+        <arguments>
+            <argument name="config" xsi:type="object">configSnapshot</argument>
+        </arguments>
+    </type>
 </config>