Refactors and fixes adding attributes in ParamBuilder

Only a single module is created and extended when adding attributes, setting of default value is done once.
Split given arguments into parts and query arguments
Refactors creation of module in ParamBuilder

The ParamBuilder class includes the Virtus module from the start, making the `attribute_set` available.
Removes Rack Test helpers and changes Elasticsearch client logger
Refactors tests for Abort Benchmark API endpoint
Adds cluster get settings API endpoint

* refactors existing specs and extracts shared example test group for a valid API response
* refactors handling of time parameter, currently it is with type String, at this point is not fully clear what the Elasticsearch API specification really defines with type `time`
Adds request method for cluster health API endpoint and tests

* refactors handling of query parameters
* adds tests to query values
Adds a put request helper method to communicate with Elasticsearch
Adds pending_tasks API endpoint with tests
Marks a failing test as pending

Still have not found a good way to enable coercion with virtus in a way that does not allow an array to a string typed parameter.
Adds cluster put settings API endpoint to client
Adds handling of source values that can be set to use in request's body
Refactors and fixes handling of source parameters

* simplifies `source_from_params` method, for now query objects are not considered
* fixes `Request.request_method` function to return valid method
* adds specs
Adds test for declaring url block twice
Adds JSON schema for cluster put settings

* adds an RSpec matcher for checking JSON schemata
* adds a shared example group for acknowledged responses
Fixes use of builder class in DSL module

Classes or modules that include the DSL get the builder property defined on `base`, not on the module.
Fixes specs for abort benchmark API function
Extends description of cluster put_settings API endpoint
Adds tests for index creation and fixes deletion of all indexes
Adds specs for create_index API function