Doc: Fixes node client section name on Java API Doc

Closes #7539
[SEARCH] Execute search reduce phase on the search threadpool

Reduce Phases can be expensive and some of them like the aggregations
reduce phase might even execute a one-off call via an internal client
that might cause a deadlock due to execution on the network thread
that is needed to handle the one-off call. This commit dispatches
the reduce phase to the search threadpool to ensure we don't wait
for the current thread to be available.

Closes #7623
[TEST] added debug info to GeoBoundsTests to try to solve build issue
[TESTS] Add explicit mappings to IndexAliasesTests.testSearchingFilteringAliasesSingleIndex

This makes sure that all shards know about the `_uid` field.
Aggregations: Adds ability to sort on multiple criteria

The terms aggregation can now support sorting on multiple criteria by replacing the sort object with an array or sort object whose order signifies the priority of the sort. The existing syntax for sorting on a single criteria also still works.

Contributes to #6917
_timestamp: enable mapper properties merging

Updates on the _timestamp field were silently ignored.
Now _timestamp undergoes the same merge as regular
fields. This includes exceptions if a property cannot
be changed.
"path" and "default" cannot be changed.

closes #5772
closes #6958
closes #7614
partially fixes #777
[TEST] added @AwaitsFix to failing StringTermsTests while I work on a fix
Make .zip and .tar.gz release artifacts contain same files.

This commit changes the build to include .exe and sigar/.dll files in
both the zip and tar artifacts.

Closes #2793
[CORE] Unify search context cleanup

Today there are two different ways to cleanup search contexts which can
potentially lead to double releasing of a context. This commit unifies
the methods and prevents double closing.

Closes #7625
[Stats] update action returns before updating stats for `NONE` operations

We keep around a noop stats indicating how many update operations ended up not updating the document (typically because it didn't change). However, the TransportUpdateAction update that counter only after returning the result. This can throw off stats check which are done immediately after, potentially causing test failures.

Closes #7639
[TEST] Don't print BWC test path - it's different on every machine
[TESTS]: create directory for heapdumps if not exists

Before the heapdump was either written in a file with the
directory name if the heapdump path ended without / or
not written at all if the path ended with /

closes #7645
Revert "[TEST] added @AwaitsFix to failing StringTermsTests while I work on a fix"

This reverts commit 18a713a2ae896e72c5821bf3f6d239ce634d1f52.
Revert "Aggregations: Adds ability to sort on multiple criteria"

This reverts commit bfedd11ffa4c48be0afd91793f491b0a8ff0ef8d.
[STORE] Write Snapshots directly to the blobstore stream

Today we serialize the snashot metadata to a byte array and then copy
the byte array to a stream. Instead this commit moves the serialization
directly to the target stream without the intermediate representation.

Closes #7637
Quiet BWC analysis test case for now.

See https://issues.apache.org/jira/browse/LUCENE-5927.
CORS: Disable by default

In order to deliver a more secure out-of-the-box configuration this commit
disables cross-origin resource sharing by default.

Closes #7151
Docs: Update plugins.asciidoc

add search by sql

Closes #7525
Core: Added the `index.query.parse.allow_unmapped_fields` setting to fail queries if they refer to unmapped fields.

The percolator and filters in aliases by default enforce strict query parsing.

Closes #7335
Simplify translog interface

get rid of readSource() entirely, it sucked, Operations should be able
to provide the source themselves.

No more TranslogStream headers, you are now required to pass an
StreamInput or StreamOutput for all operations, which means no extra
state is needed and no need to construct new versions when detecting the
version.

Read and write translog op sizes in TranslogStreams

Previously we handled these integers outside of the translog stream
itself, which was very unclean because other code had to know about
reading the size, or about writing the correct header sometimes.

There is some additional code in LocalIndexShardGateway to handle the
legacy case for older translogs, because we need to read and discard the
size in order to maintain the compatibility for the streaming
operations (they did not read or write the size for 1.3.x and earlier).

Additionally, we need to handle a case where the header is truncated
when recovering from disk

Use a NoopStreamOutput instead of byte arrays

Instead of writing translog operations to a temporary byte array and
then writing that byte array to the stream, we now write the operation
twice, once to a No-op stream to get the size, then again to the real
size.

This trades a little more CPU usage for less memory usage.