The progress bar will look like this:

![1___spark_job__85_250_finished__4_are_running___java_](https://cloud.githubusercontent.com/assets/40902/4854813/a02f44ac-6099-11e4-9060-7c73a73151d6.png)

In the right corner, the numbers are: finished tasks, running tasks, total tasks.

After the stage has finished, it will disappear.

The progress bar is only showed if logging level is WARN or higher (but progress in title is still showed), it can be turned off by spark.driver.showConsoleProgress.

Author: Davies Liu <davies@databricks.com>

Closes #3029 from davies/progress and squashes the following commits:

95336d5 [Davies Liu] Merge branch 'master' of github.com:apache/spark into progress
fc49ac8 [Davies Liu] address commentse
2e90f75 [Davies Liu] show multiple stages in same time
0081bcc [Davies Liu] address comments
38c42f1 [Davies Liu] fix tests
ab87958 [Davies Liu] disable progress bar during tests
30ac852 [Davies Liu] re-implement progress bar
b3f34e5 [Davies Liu] Merge branch 'master' of github.com:apache/spark into progress
6fd30ff [Davies Liu] show progress bar if no task finished in 500ms
e4e7344 [Davies Liu] refactor
e1f524d [Davies Liu] revert unnecessary change
a60477c [Davies Liu] Merge branch 'master' of github.com:apache/spark into progress
5cae3f2 [Davies Liu] fix style
ea49fe0 [Davies Liu] address comments
bc53d99 [Davies Liu] refactor
e6bb189 [Davies Liu] fix logging in sparkshell
7e7d4e7 [Davies Liu] address commments
5df26bb [Davies Liu] fix style
9e42208 [Davies Liu] show progress bar in console and title