Change default value to allow code coverage on non-app files.

Don't default to app, as it prevents generating code coverage for core
and plugin files.

Fixes #6533

lib/Cake/TestSuite/CakeTestSuiteDispatcher.php

@@ -37,7 +37,7 @@ class CakeTestSuiteDispatcher {
 		'codeCoverage' => false,
 		'case' => null,
 		'core' => false,
-		'app' => true,
+		'app' => false,
 		'plugin' => null,
 		'output' => 'html',
 		'show' => 'groups',