Add search to DiscoveryIO

* use ElasticIO.Result as SearchResult. It is generic enough.
* simple method in interface to return SearchResults.
* retool tests.
Build the query properly.
Merge pull request #342 from gdusbabek/esio_search

Search specification of for discovery interface.
Initial commit which adds HttpMetricsIndexHandler
Add the HttpMetricsIndexHandler
Use the correct class name in logger for metrics index handler
Merge pull request #343 from chinmay-gupte/chinmay/add_BF_API_support_for_metrics_discovery

WIP: Add query support for metrics discovery