As a user, I can update existing Test Runs using the Xray REST API

The Xray REST API should provide a way for users to update existing Test Runs.

When updating Test Step statuses, or example statuses, the overall execution status for the Test Run must be calculated.

These new methods will provide a way for users to incrementally update Test Run results instead of importing final results only with the existing API: http://confluence.xpand-it.com/display/XRAY/REST+API#RESTAPI-XrayJSONresults