MAGETWO-54054: Compiler performance optimization

 - MAGETWO-50778: [Github][PR] Add cache of configuration files list #1628
 - Merge commit 'refs/pull/1628/head' of github.com:magento/magento2 into MAGETWO-50778

# Conflicts:
#	lib/internal/Magento/Framework/Module/Dir/Reader.php

Author: Volodymyr Kublytskyi

lib/internal/Magento/Framework/Module/Dir/Reader.php

@@ -46,6 +46,13 @@ class Reader
      */
     protected $readFactory;
 
+    /**
+     * Cache storage
+     *
+     * @var array
+     */
+    protected $cache = [];
+
     /**
      * @param Dir $moduleDirs
      * @param ModuleListInterface $moduleList
@@ -72,7 +79,10 @@ public function __construct(
      */
     public function getConfigurationFiles($filename)
     {
-        return $this->fileIteratorFactory->create($this->getFiles($filename, Dir::MODULE_ETC_DIR));
+        if (isset($this->cache[$filename])) {
+            return $this->cache[$filename];
+        }
+        return $this->cache[$filename] = $this->fileIteratorFactory->create($this->getFiles($filename, Dir::MODULE_ETC_DIR));
     }
 
     /**