Aggregations: change to default shard_size in terms aggregation

The default shard size in the terms aggregation now uses BucketUtils.suggestShardSideQueueSize() to set the shard size if the user does not specify it as a parameter.

Closes #6857
Internal: streamline use of IndexClosedException when executing operation on closed indices

Single index operations to use the newly added IndexClosedException introduced with #6475. This way we can also fail faster when we are trying to execute operations on closed indices and their use is not allowed (depending on indices options). Indices blocks are still checked but we can already throw error while resolving indices (MetaData#concreteIndices).

Effectively this change also affects what we return when using one of the following apis: analyze, bulk, index, update, delete, explain, get, multi_get, mlt, term vector, multi_term vector. We now return `{"error":"IndexClosedException[[test] closed]","status":403}` instead of `{"error":"ClusterBlockException[blocked by: [FORBIDDEN/4/index closed];]","status":403}`.

Closes #6988
[REFACTOR] TransportActions

Get rid of boilerplate code for handling transport actions.
Make these transport actions extend HandledTransportAction where this code
now lives.
[TESTS] Add more assertions to SimpleFacetsTests.
Made `_source` parsing in `top_hits` aggregation consistent with regular `_source` parsing in search api.

Closes #6997
[TEST] Don't randomize preference PRIMARY it might not try replicas depending on the clusterstate
Speed up string sort with custom missing value

Today if the user supplies a custom missing value for a string sort,
we do it in an extremely slow way, not using ordinals but dereferencing
bytes for every document. Ordinals are only used if the missing value
is _first or _last.

Instead, use ordinals with custom missing values too.

Closes #7005
Aggregations: Better JSON output scoping

Before this change each aggregation had to output an object field with its name and write its JSON inside that object.  This allowed for badly behaved aggregations which could write JSON content in the root of the 'aggs' object.  this change move the writing of the aggregation name to a level above the aggregation itself, ensuring that aggregations can only write within there own scope in the JSON output.

Closes #7004
[Benchmark] Make TermsAggregationSearchBenchmark fairer to uninverted field data.

The benchmark indexes 200 unique full-width longs. For uninverted field data
we try to use the most memory-efficient storage, and in that case it would use
two arrays: one for the doc->ordinals mapping and one for the ordinal->value
mapping. Which is slower than what doc values do by storing directly the
mapping from docs to values.
Internal: expose the indices names every action relates to if applicable

Added two new interfaces:
1) IndicesRequest that allows to retrieve the indices the request relates to in a generic manner, together with the indices options that tell how they are going to get resolved and expanded
2) CompositeIndicesRequest for compound requests that hold multiple indices request like MultiSearchRequest, MultiGetRequest, MultiTermVectorsRequest, BulkRequest, BenchmarkRequest, PercolateRequest, MultiPercolateRequest and MoreLikeThisRequest

Taken the chance to streamline the indices options and add them to every request where it makes sense (although they can't be changed from the outside), rather than leaving them implicit in the related TransportAction when indices get expanded (tipycally MetaData#concreteIndices or MetaData#concreteSingleIndex). Added IndicesOptions parameter to MetaData#concreteSingleIndex to make sure it is taken from the request, where the information belongs, instead of hardcoded within MetaData. The concreteSingleIndex method remains but it's just a utility method that returns a single index instead of an array and complains otherwise.

Also made sure NPE is never thrown when setting indices(null) to IndicesAliasesRequest, similar to what SearchRequest does.

Closes #6933
remove use of recycled set in filters eviction
closes #7012
Add `wait_if_ongoing` option to _flush requests

This commit adds the ability to force blocking on the flush operaition
to make sure all files have been written and synced to disk. Without
this option a flush might be executing at the same time causing the
current flush to fail and return before all files being synced.

Closes #6996