MAGETWO-38383: Increase Unit Test Code Coverage

-Removed unnecessary is_readable check

Author: Ian Daszkowski

setup/src/Magento/Setup/Fixtures/FixtureModel.php

@@ -105,11 +105,6 @@ public function reindex(OutputInterface $output)
      */
     public function loadFixtures()
     {
-        if (!is_readable(__DIR__)) {
-            throw new \Exception(
-                'Fixtures set directory `' . __DIR__ . '` is not readable or does not exists.'
-            );
-        }
         $files = glob(__DIR__ . DIRECTORY_SEPARATOR . self::FIXTURE_PATTERN);
 
         foreach ($files as $file) {