[TEST] Verify if clear cache request went to all shards.
[DOCS] Move benchmark API to 1.4
Threadpool Info: Allow to serialize negative thread pool sizes

As a SizeValue is used for serializing the thread pool size, a negative number
resulted in throwing an exception when deserializing (using -ea an assertionerror
was thrown).

This fixes a check for changing the serialization logic, so that negative numbers are read correctly, by adding an internal UNBOUNDED value.

Closes #6325
Closes #5357
Add read/write lock semantics to KeyedLock
[FIELDDATA] Use KeyedLock in IndexFieldDataService

Today we synchronize when updating the IndexFieldDataService
datastructures. This might unnecessarily block progress if multiple
request need different fielddata instance for different fields.

This commit also fixes clear calls to actually consistently clear
the caches in the case of an exception.

Closes #6855
REST: Renamed indexed_script and indexed_template specs

The file name of the REST specs should be the same as
the endpoint which it documents.
REST: Fixed indexed script/template tests

The clients don't have access to the error message
for matching purposes.  Rewritten tests to work
with the clients
Serialization: Fix bwc issue by falling back to old threadpool serialization

This fixes an issue introduced by the serialization changes in #6486
which are not needed at all. Node that the serialization itself is not broken
but the TransportClient uses its own version on initial connect and getting
the NodeInfos.