Test: add test case verifying updating merge IO throttle settings works

Closes #6842
[Test] testSingleNodeWithFlush should wait for yellow

O.w. it can restart a node before all primaries are started , leading to a red state down the road...
Indexed Scripts/Templates: Add support for storing/deleting/getting scripts/template from an index.

This change allow elasticsearch users to store scripts and templates in an index for use at search time.
Scripts/Templates are stored in the .scripts index. The type of the events is set to the script language.
Templates use the mustache language so their type is be "mustache".
Adds the concept of a script type to calls to the ScriptService types are INDEXED,INLINE,FILE.
If a script type of INDEXED is supplied the script will be attempted to be loaded from the indexed, FILE will
look in the file cache and INLINE will treat the supplied script argument as the literal script.
REST endpoints are provided to do CRUD operations as is a java client library.
All query dsl points have been upgraded to allow passing in of explicit script ids and script file names.
Backwards compatible behavior has been preserved so this shouldn't break any existing querys that expect to
pass in a filename as the script/template name. The ScriptService will check the disk cache before parsing the
script.

Closes #5921 #5637 #5484
Docs: Update query-string-syntax.asciidoc

Closes #6853
[TEST] fix compile problems on Java 8
[TEST] Fix test issues with branches still using mvel as default scripting language
[TEST] Fix test relying on order of json for matching