Updated es_release_notes script to replace backticks with code tags
Plugin Lucene version checker: use `Lucene.parseVersionLenient`

With commit 07c632a2d4dbefe44e8f25dc4ded6cf143d60e41, we now have a new Lucene.parseVersionLenient(String, Version) method which tries to find an existing Lucene version based on the two first digits X.Y of X.Y.Z String.
Internal: use AtomicInteger instead of volatile int for the current action filter position

Also improved filter chain tests to not rely on execution time, and made filter chain tests look more similar to what happens in reality by removing multiple threads creation in testTooManyContinueProcessing (something we don't support anyway, makes little sense to test it).

Closes #7021
Rest: fixed filters execution order to be from lowest to highest rather than the other way around

Closes #7019
[TESTS] fix circuit breaker tests for remote clusters and bwc

Adds additional version checks in NodeStats for older versions

When using an external cluster (backwards compatibility tests), the act
of checking the request breaker requires a network buffer, which
increments the breaker. This change only checks the request breaker in
InternalTestCluster and uses Guice to retrieve it instead of
a (possible) network request.

Also removed the now unused InternalCircuitBreakerService class
Add [1.3.2] version constant
Transport Client: fixed the node retry mechanism which could fail without trying all the connected nodes

The RetryListener was notified twice for each single failure, which caused some additional retries, but more importantly was making the client reach the maximum number of retries (number of connected nodes) too quickly, meanwhile ongoing retries which could succeed were not completed yet.

The TransportService used to throw ConnectTransportException due to throwConnectException set to true, and also notify the listener of any exception received from a separate thread through the request holder.

Simplified exception handling by just removing the throwConnectException option from the TransportService, used only in the transport client. The transport client now relies solely on the request holder to notify of failures and eventually retry.

Closes #6829
Transport client: don't add listed nodes to connected nodes list in sniff mode

This commit effectively reverts e1aa91d , as it is not needed anymore to add the original listed nodes. The cluster state local call made will in fact always return at least the local node (see #6811).

There were a couple of downsides caused by putting the original listed nodes among the connected nodes:
1) in the following retries, they weren't seen as listed nodes anymore, thus the light connect wasn't used
2) among the connected nodes some were "bad" duplicates as they are already there and don't contain all needed info for each node. This was causing serialization problems for instance given that the node version was missing on the `DiscoveryNode` object.

Closes #7067
Remove NEST from community clients
[Docs] Add link to .NET client docs
Docs: Correct JSONP comment in config file

Due to the change of disabling JSONP by default in 1.3 we also need to
change the description in the configuration file.

Closes #7069
[TEST] Add basic upgrade test script

This commit adds a basic full cluster restart upgrade script that tests
upgrades of elasticsearch across major version. In contrast to the BWC
tests we are running using the java test framework this test uses a python
script as well as the REST APIs to ensure upgrades across major version work and
indices are compatible.

The upgrade test starts 2 or more nodes of an old elasticserach version, indexes
a random number of documents into the running nodes and executes a full cluster restart.
After the nodes are recovered a small set of basic checks are executed to ensure all
documents are still searchable and field data can be loaded etc.