andrewor14 squito Dead Executors should also be displayed on Executor Tab.
as following:
![image](https://cloud.githubusercontent.com/assets/545478/11492707/ae55d7f6-982b-11e5-919a-b62cd84684b2.png)

Author: Lianhui Wang <lianhuiwang09@gmail.com>

This patch had conflicts when merged, resolved by
Committer: Andrew Or <andrew@databricks.com>

Closes #10058 from lianhuiwang/SPARK-7729.