[master] fix testHLog#testAppendClose

Author: fan

Summary: Increase sleep time for DFS to shut down cleanly.

Test Plan: Unit test pass

Reviewers: liyintang, adela

Reviewed By: liyintang

CC: hbase-eng@

Differential Revision: https://phabricator.fb.com/D980500

Task ID: 2729130

git-svn-id: https://svn.apache.org/repos/asf/hbase/branches/0.89-fb@1527014 13f79535-47bb-0310-9956-ffa450edef68