docs: add pgp key to repositories page
Plugins: Plugin failed to load since #8666

The method Path.endsWith(String s) doesn't work exactly the same way as String.endsWith() (see http://docs.oracle.com/javase/7/docs/api/java/nio/file/Path.html#endsWith(java.nio.file.Path)). This blocks the loading of plugins.
Merge branch 'fix/plugins-loading'
[ENGINE] Add engine lifecycle store reference to EngineHolder

This commit add the engines reference to the store out of the actual
implementation into the hodler since the holder manages the actual lifcycle.
Engine internal references like per searcher or per recovery are kept inside
the actual implemenation since the have a different lifecycle.
Test: fix this test to work in IntelliJ
fix cache key methods on leaf reader
Add test that ES filterreader getCoreCacheKey() behaves correctly.

Closes #8831.
Stats: Add more fine grained memory stats from Lucene segment reader.

This is a start to exposing memory stats improvements from Lucene 5.0.
This adds the following categories of Lucene index pieces to index stats:
* Terms
* Stored fields
* Term Vectors
* Norms
* Doc values
Tests: Additional test for memory stats api.
[TEST] Beef up InternalEngineTest and remove bogus timeouts
Ban java.io.File in tests.

Restrict use of java.io.File to 5 methods (excluded), but otherwise ban.
This is a prerequisite to do any mocking here.

I don't try to do any heavy cleanup on these tests, I am not familiar with them.
So this is mostly a rote straightforward conversion.

Closes #8836
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.