As a machine, the REST API should provide Test and TestExecution keys in testruns

In the REST API, test runs should provide the keys for the related Test and Test Execution.
This affects the endpoints:

• /rest/raven/1.0/api/testrun/ {id}
• /rest/raven/1.0/api/testrun/
• /rest/raven/1.0/api/test/ {key}

  /testruns