Add a startup timeout limit for the plug-in application. Currently the timeout is 10 seconds.

Starting a bad plugin while EMQX is running will result in a thrown runtime error.
When EMQX is closed and restarted, the main starting process may hang due to the the plugin application to start failures.

Maybe restarting with modified:
- Modifed config file: make the bad plugin enabled.
- Add a plugin with bad plugin config.