Fixed test that relied on internal document ordering.

Lucene might internally tie-break on low level doc-Ids which
can change depending on merges etc. and test timings. No test should
rely on the actual order if scores are identical.
better handling of failures in transport to catch assertions
make sure we also catch assertions (well Throwable) in our transport layer and properly log or callback the exception handler in that case
Add a "score_mode" parameter to rescoring query.

Default value is "total", possible values are: "max", "min", "avg",
"multiply" and "total".

- "total": the final score of a document is the sum of the original
  query score with the rescore query score.
- "max": only the highest score count.
- "min": only the lowest score is kept (if the document doesn't match
  the rescore query, the original query score is used).
- "avg": average of both scores
- "multiply": product of both scores

Closes #3258
better handling of failures in transport to catch assertions
move wrapping the stream into the try block, even though its unlikely they will throw a failure, better be safe...
Only check if ttl purger has deleted the docs when the delete count in indexing stats has been increased.
pass the codec to fix index
its not used in Lucene fix index implementation, but just in case, pass it because we can (tm).
Added support for percolating an existing document.

The percolate an existing document feature executes an internal get operation to get the source of the document to percolate.

All options for percolating an existing document:
* `id` - The id of the document to percolate.
* `type` - The type of the document to percolate.
* `index` - The index to fetch the document to percolate from.
* `routing` - The routing value to use to retrieve the document to percolate.
* `preference` - Which shard to prefer (defaults to `_local`).
* `version` - Enables a version check. If the fetched document's version isn't equal to the specified version then the request fails with a version conflict and the percolation request is aborted.

All the option can be specified inside the `get` body part or via query string arguments.
Internally the percolate api will issue a get request for fetching the`_source` of the document to percolate.

For this feature to work the `_source` for documents to percolate need to be stored.

Closes #3380
cleanup signatures file
enable sys out check + remove unused code
Don't allow unallocated indexes to be closed.

Closes #3313
[snapshot/restore] Add ability to register snapshot repositories
[snapshot/restore] Add support for Repository Instantiation
[snapshot/restore] Add snapshot creation mechanism
[snapshot/restore] Rename snapshot endpoint to repository
[snapshot/restore] Add snapshot status update mechanism
[snapshot/restore] Add snapshot simple end-to-end snapshotting test
[snapshot/restore] Add basic file system store implementation
[snapshot/restore] Add file snapshotting
[snapshot/restore] First stage or repository refactoring - make them static
[snapshot/restore] Cleanup after refactoring