test: use process.features.debug in common module

Replace process.config.target_defaults.default_configuration check with
process.features.debug.

Refs: nodejs#4431 (comment)

Author: Trott

test/common/index.js

@@ -340,7 +340,7 @@ exports.spawnSyncPwd = function(options) {
 };
 
 exports.platformTimeout = function(ms) {
-  if (process.config.target_defaults.default_configuration === 'Debug')
+  if (process.features.debug)
     ms = 2 * ms;
 
   if (global.__coverage__)