SPARK-2602 [BUILD] Tests steal focus under Java 6

As per https://issues.apache.org/jira/browse/SPARK-2602 , this may be resolved for Java 6 with the java.awt.headless system property, which never hurt anyone running a command line app. I tested it and seemed to get rid of focus stealing.

Author: Sean Owen <srowen@gmail.com>

Closes #1747 from srowen/SPARK-2602 and squashes the following commits:

b141018 [Sean Owen] Set java.awt.headless during tests
(cherry picked from commit 33f167d762483b55d5d874dcc1e3075f661d4375)

Signed-off-by: Patrick Wendell <pwendell@gmail.com>
SPARK-2414 [BUILD] Add LICENSE entry for jquery

The JIRA concerned removing jquery, and this does not remove jquery. While it is distributed by Spark it should have an accompanying line in LICENSE, very technically, as per http://www.apache.org/dev/licensing-howto.html

Author: Sean Owen <srowen@gmail.com>

Closes #1748 from srowen/SPARK-2414 and squashes the following commits:

2fdb03c [Sean Owen] Add LICENSE entry for jquery
(cherry picked from commit 9cf429aaf529e91f619910c33cfe46bf33a66982)

Signed-off-by: Patrick Wendell <pwendell@gmail.com>
[Minor] Fixes on top of #1679

Minor fixes on top of #1679.

Author: Andrew Or <andrewor14@gmail.com>

Closes #1736 from andrewor14/amend-#1679 and squashes the following commits:

3b46f5e [Andrew Or] Minor fixes
(cherry picked from commit 3dc55fdf450b4237f7c592fce56d1467fd206366)

Signed-off-by: Patrick Wendell <pwendell@gmail.com>