Docs: Update repositories.asciidoc

1. Enable the repository using "add-apt-repository" to avoid this error "No command 'deb' found".
2. Adding "sudo" to update and install command.

Closes #8691
Docs: Fix the wording for inner hits a bit

Closes #8747
[TEST] compare strings and strings - leftover from Path API refactoring
[TEST] LoggingListener to restore the initial logger levels after any modification

Modifications to LoggingListener pushed with #8820 caused the original logger levels not to be reset after modifications, as the new state was saved for restore instead of the previous one.

 Added unit tests for LoggingListener as well.

Closes #8845
[TEST] Restore test logging level after test is done
Core: also log byte size and doc count when we log slow merges

Closes #8855

Closes #8853
Use Lucene version string in main rest action

This commit removes the deprecated constant for the main
version and uses the real lucene version we are running instead.
Behind the scenes the same value was used and is now obsolet.
Add more trace logging to gateway translog recovery
Core: put []'s around the values in the slow-merge log message
[TEST] Use private store for a test private engine

The test was using the same store as the suite level engine which caused
problems with write locks in some cases.

Closes #8880
[CORE] Drop support for state written pre 0.90

Today we have several upgrade methods that can read state written
pre 0.90 or even pre 0.19. Version 2.0 should not support these state
formats. Users of these version should upgrade to a 1.x or 0.90.x version
first.

Closes #8850
[TEST] wait for yellow to avoid searching while relocating

After upgrading shard might start relocating again. If there are no
replicas the cluster state of a node might not be up to data for
a few miliseconds and direct a search request to a node that does not
have the shard anymore. This result in the following test failures:

1> java.lang.AssertionError: Count is 99 but 101 was expected.  Total shards: 13 Successful shards: 12 & 0 shard failures:
1>     __randomizedtesting.SeedInfo.seed([1932F73B458703CA:6F4FAD3DAC55591C]:0)
1>     [...org.junit.*]
1>     org.elasticsearch.test.hamcrest.ElasticsearchAssertions.assertHitCount(ElasticsearchAssertions.java:184)
1>     org.elasticsearch.bwcompat.BasicBackwardsCompatibilityTest.testIndexRollingUpgrade(BasicBackwardsCompatibilityTest.java:358)

Waiting for relocation finished should fix this.
Docs: use https to download the gpg public key

Closes #8818
[TEST] Reset test logger to default level
[ENGINE] Fix updates dynamic settings in InternalEngineHolder

After the refactoring in #8784 some settings didn't get passed to the
actual engine and there exists a race if the settings are updated while
the engine is started such that the actual starting engine doesn't see
the latest settings. This commit fixes the concurrency issue as well as
adds tests to ensure the settings are reflected.
[GEO] Fix for NPE enclosed in SearchParseException for a "geo_shape" filter or query

This fix adds better error handling for parsing multipoint, linestring, and polygon GeoJSONs.  Current logic throws a NPE when parsing a multipoint, linestring, or polygon that does not comply with the GeoJSON specification. That is, if a user provides a single coordinate instead of an array of coordinates, or array of linestrings, the ShapeParser throws a NPE wrapped in a SearchParseException instead of a more useful error message.

Closes #8432
[core] add best_compression option for Lucene 5.0

Upgrades lucene to latest, and supports the BEST_COMPRESSION parameter
now supported (with backwards compatibility, etc) in Lucene.
This option uses deflate, tuned for highly compressible data.

index.codec::
The default value compresses stored data with LZ4 compression, but
this can be set to best_compression for a higher compression ratio,
at the expense of slower stored fields performance.

IMO its safest to implement as a named codec here, because ES already
has logic to handle this correctly, and because its unrealistic to have
a plethora of options to Lucene's default codec... we are practically
limited in Lucene to what we can support with back compat, so I don't
think we should overengineer this and add additional unnecessary plumbing.

See also:
https://issues.apache.org/jira/browse/LUCENE-5914
https://issues.apache.org/jira/browse/LUCENE-6089
https://issues.apache.org/jira/browse/LUCENE-6090
https://issues.apache.org/jira/browse/LUCENE-6100

Closes #8863
Test: create private store for these test cases
Mappings: Fix Get field mapping api with pretty flag

Closes #6552
[ENGINE] Remove engine related command classes

Todaqy we pass structs to the engine to call optimize / refresh and flush.
This commit cleans up this logic to reduce complexity in the engine.