[SPARK-20514][CORE] Upgrade Jetty to 9.3.11.v20160721

[markgrover]

Upgrade Jetty so it can work with Hadoop 3 (alpha 2 release, in particular).
Without this change, because of incompatibily between Jetty versions,
Spark fails to compile when built against Hadoop 3

How was this patch tested?

Unit tests being run.

[markgrover]

I am running unit tests locally and while the run hasn't finished, it's looking pretty good so far. I think it'd be good to get Jenkins to run the tests here anyways so putting a PR sooner than later.

[vanzin]

The PR title says one thing but your code says another.

[markgrover]

Ah, thanks, there was some confusion about this. I have fixed the JIRA title and the PR title to match up with the actual code - which uses the exact same version as Apache Hadoop (9.3.11.v20160721).

[srowen]

CC @zsxwing as it touches Jetty.
This is probably OK, even though it will impact the classpath for user apps and Jetty could have some non-trivial changes. I agree there's good reason to do this though.

[vanzin]

it will impact the classpath for user apps

Jetty is shaded in Spark.

[zsxwing]

cc @yhuai

[SparkQA]

Test build #76244 has finished for PR 17790 at commit ecfb8e3.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[vanzin]

LGTM.

[markgrover]

Thanks for the review!

[vanzin]

If there are no more concerns I'll push this in the PM.

[zsxwing]

LGTM.

[vanzin]

Merging to master / 2.2.