[TESTS] Update PHPUnit config to use coverage cache

phpunit.xml.dist

@@ -5,11 +5,11 @@
          backupGlobals="false"
          colors="true"
          bootstrap="tests/bootstrap.php"
+         cacheDirectory="var/phpunit/coverage_cache"
+         cacheResultFile="var/phpunit/result_cache"
          stopOnFailure="true"
          stopOnError="true"
-         cacheResult="true"
-         cacheResultFile=".phpunit_cache"
-         executionOrder="defects">
+         cacheResult="true">
   <coverage processUncoveredFiles="true">
     <include>
       <directory suffix=".php">src</directory>