[SPARK-14254][CORE] Add logs to help investigate the network performance

## What changes were proposed in this pull request?

It would be very helpful for network performance investigation if we log the time spent on connecting and resolving host.

## How was this patch tested?

Jenkins unit tests.

Author: Shixiong Zhu <shixiong@databricks.com>

Closes #12046 from zsxwing/connection-time.