HUE-8302 [jobbrowser] Failed to fetch logs for Spark jobs

Review Request #12959 - Created May 17, 2018 and updated

Ivan Dzikovsky

This issue caused because in some case executor variable was used before assignment in SparkHistoryServerApi.get_executors_loglinks, and after resolving this problem, I've also faced with following errors in Hue logs:

[17/May/2018 09:28:15 +0000] yarn_models  WARNING  Spark resolve tracking URL returned a failed response: 'str' object is not callable
[17/May/2018 09:28:44 +0000] yarn_models  WARNING  Failed to resolve Spark Job's actual tracking URL: 'NoneType' object has no attribute 'strip'

That was caused because SparkJob._execute method expects to get function as argument, but string was passed to this method in SparkJob._resolve_tracking_url method body.