[SPARK-17558] Bump Hadoop 2.7 version from 2.7.2 to 2.7.3

## What changes were proposed in this pull request?
This patch bumps the Hadoop version in hadoop-2.7 profile from 2.7.2 to 2.7.3, which was recently released and contained a number of bug fixes.

## How was this patch tested?
The change should be covered by existing tests.

Author: Reynold Xin <rxin@databricks.com>

Closes #15115 from rxin/SPARK-17558.