Expose executorId to `ReceiverInfo` and UI since it's helpful when there are multiple executors running in the same host. Screenshot:

<img width="1058" alt="screen shot 2015-11-02 at 10 52 19 am" src="https://cloud.githubusercontent.com/assets/1000778/10890968/2e2f5512-8150-11e5-8d9d-746e826b69e8.png">

Author: Shixiong Zhu <shixiong@databricks.com>
Author: zsxwing <zsxwing@gmail.com>

Closes #9418 from zsxwing/SPARK-11333.