[SPARK-12755][CORE] Stop the event logger before the DAG scheduler

[SPARK-12755][CORE] Stop the event logger before the DAG scheduler to avoid a race condition where the standalone master attempts to build the app's history UI before the event log is stopped.

This contribution is my original work, and I license this work to the Spark project under the project's open source license.

Author: Michael Allman <michael@videoamp.com>

Closes #10700 from mallman/stop_event_logger_first.