[CORE] Free pending search contexts if index is closed

Today we hold on to search context reference if they are not cleaned
up for a while until a reaper thread trashes them if they timed out.
This commit removes all pending contexts once the index is closed to release
resources and filehandles immediatly once the index is closed.
Remove NoneGateway, NoneGatewayAllocator, & NoneGatewayModule

Always use the LocalGateway* equivalents

We already check in the LocalGateway whether a node is a client node, or
is not master-eligible, and skip writing the state there. This allows us
to remove this code that was previously used only for tribe nodes (which
are not master eligible anyway and wouldn't write state) and in
tests (which can shake more bugs out)