Added base Request class for read operations that usually happen on the master but can be executed locally.
Added base TransportAction class for master read operations that execute locally or not depending on the request class (local flag).

Added support for local flag where missing, in a backwards compatible manner:
     - IndicesExistsRequest
     - GetAliasesRequest (get alias api, aliases exist api)
     - TypesExistsRequest
     - GetIndexTemplatesRequest (get template, template exists)
     - GetSettingsRequest
     - GetRepositoriesRequest
     - PendingClusterTasks

 Added parsing of the local flag where missing in Rest*Action.

 Updated SPEC adding local flag param where missing and added REST tests that contain use of the local flag where it was just added.

Closes #3345