bugfix: Wrong "Duration" in "Active Stages" in stages page

If a stage which has completed once loss parts of data, it will be resubmitted. At this time, it appears that stage.completionTime > stage.submissionTime.

Author: shiyun.wxm <shiyun.wxm@taobao.com>

Closes #170 from BlackNiuza/duration_problem and squashes the following commits:

a86d261 [shiyun.wxm] tow space indent
c0d7b24 [shiyun.wxm] change the style
3b072e1 [shiyun.wxm] fix scala style
f20701e [shiyun.wxm] bugfix: "Duration" in "Active Stages" in stages page
SPARK-1203 fix saving to hdfs from yarn

Author: Thomas Graves <tgraves@apache.org>

Closes #173 from tgravescs/SPARK-1203 and squashes the following commits:

4fd5ded [Thomas Graves] adding import
964e3f7 [Thomas Graves] SPARK-1203 fix saving to hdfs from yarn
Merge github.com:apache/spark

Conflicts:
	core/src/main/scala/org/apache/spark/ui/jobs/StageTable.scala