[Scripts] GroovyScriptEngineService don't create ScoreAccess if lookup is null
Netty: Refactoring to make MessageChannelHandler extensible

Small refactorings to make the MessageChannelHandler more extensible.
Also allowed access to the different netty pipelines

Closes #6889
bin/plugin removes itself

If you call `bin/plugin --remove es-plugin` the plugin got removed but the file `bin/plugin` itself was also deleted.

We now don't allow the following plugin names:

* elasticsearch
* plugin
* elasticsearch.bat
* plugin.bat
* elasticsearch.in.sh
* service.bat

Closes #6745
[TEST] Use array* helper assert methods instead of verifying the array directly
[TEST] Fixed intermittent failure due to lack of mapping
Refactoring: Rename FieldMapper.termsFilter to fieldDataTermsFilter.

FieldMapper has two methods
`Filter termsFilter(List values, @Nullable QueryParseContext)` which is supposed
to work on the inverted index and
`Filter termsFilter(QueryParseContext, List, QueryParseContext)` which is
supposed to work on field data. Let's rename the second one to
`fieldDataTermsFilter` and remove the unused `QueryParseContext`.

Close #6888