[SPARK-7161] [HISTORY SERVER] Provide REST api to download event logs fro...

...m History Server

This PR adds a new API that allows the user to download event logs for an application as a zip file. APIs have been added to download all logs for a given application or just for a specific attempt.

This also add an additional method to the ApplicationHistoryProvider to get the raw files, zipped.

Author: Hari Shreedharan <hshreedharan@apache.org>

Closes #5792 from harishreedharan/eventlog-download and squashes the following commits:

221cc26 [Hari Shreedharan] Update docs with new API information.
a131be6 [Hari Shreedharan] Fix style issues.
5528bd8 [Hari Shreedharan] Merge branch 'master' into eventlog-download
6e8156e [Hari Shreedharan] Simplify tests, use Guava stream copy methods.
d8ddede [Hari Shreedharan] Remove unnecessary case in EventLogDownloadResource.
ffffb53 [Hari Shreedharan] Changed interface to use zip stream. Added more tests.
1100b40 [Hari Shreedharan] Ensure that `Path` does not appear in interfaces, by rafactoring interfaces.
5a5f3e2 [Hari Shreedharan] Fix test ordering issue.
0b66948 [Hari Shreedharan] Minor formatting/import fixes.
4fc518c [Hari Shreedharan] Fix rat failures.
a48b91f [Hari Shreedharan] Refactor to make attemptId optional in the API. Also added tests.
0fc1424 [Hari Shreedharan] File download now works for individual attempts and the entire application.
350d7e8 [Hari Shreedharan] Merge remote-tracking branch 'asf/master' into eventlog-download
fd6ab00 [Hari Shreedharan] Fix style issues
32b7662 [Hari Shreedharan] Use UIRoot directly in ApiRootResource. Also, use `Response` class to set headers.
7b362b2 [Hari Shreedharan] Almost working.
3d18ebc [Hari Shreedharan] [WIP] Try getting the event log download to work.