Added more trace and debug logging
[TEST] more assertAcked in SharedClusterShapshotRestoreTests
Add plugin class space isolation

Each plugin is now loaded in its own classloader to prevent class
conflicts when loading different versions of the same library. It
 is enabled by default and is configurable through
 `plugins.isolation` settings .Additionally, each plugin can
change its own isolation through the `isolation` property in
`es-plugin.properties`- if not specified, the global setting in
ES applies.

Closes #5261
[TEST] Add version and master_node parameter to _cluster/state
[TEST] Dynamically extract node ID for test
fix failing IsolatedPluginTests (change numNodes to 0)

(cherry picked from commit f26a369a78ade032df44fcf331f378644f74b9ea)
[DOCS] Fixed added[] tag version number
make test assertions relative in IsolatedPluginTests

relates to #5621
[TEST] skip explain reroute REST test until param substitution is implemented
Clarify range aggregations
Remove same-thread checks when recycling (see #5254).
Prevent page-tracking checks from spreading across tests.
Reuse pages more agressively in BigArrays.

Pages are now going to be reused when the size of the array is greater than
${page_size}/2 (as opposed to ${page_size} currently).

Close #5299
fix incorrect array search in test (by sorting it first)

relates to #5621
fix typo causing incorrect plugin properties lookup in jars

relates #5261
[TEST] added support for replacing stashed values within objects and lists in our REST tests
[DOCS] Better document the limitation of nested objects.
Percentiles aggregation.

A new metric aggregation that can compute approximate values of arbitrary
percentiles.

Close #5323
Fix test bug: a too low compression level can make accuracy terrible.
[DOCS] Java API JSON typo