I suppose I could find the System.setProperty that is causing this and move it to the main thread...here are the (quickly grepped) candidates:

```
> git grep System.setProperty -- core/src/main/
core/src/main/scala/org/apache/spark/SparkContext.scala:    System.setProperty("spark.driver.host", Utils.localHostName())
core/src/main/scala/org/apache/spark/SparkContext.scala:    System.setProperty("spark.driver.port", "0")
core/src/main/scala/org/apache/spark/SparkEnv.scala:      System.setProperty("spark.driver.port", boundPort.toString)
core/src/main/scala/org/apache/spark/SparkEnv.scala:      System.setProperty("spark.hostPort", hostname + ":" + boundPort)
core/src/main/scala/org/apache/spark/SparkEnv.scala:    System.setProperty("spark.fileserver.uri", httpFileServer.serverUri)
core/src/main/scala/org/apache/spark/broadcast/HttpBroadcast.scala:    System.setProperty("spark.httpBroadcast.uri", serverUri)
core/src/main/scala/org/apache/spark/deploy/FaultToleranceTest.scala:  System.setProperty("spark.driver.host", "172.17.42.1") // default docker host ip
core/src/main/scala/org/apache/spark/deploy/FaultToleranceTest.scala:    System.setProperty("spark.driver.port", "0")
core/src/main/scala/org/apache/spark/executor/CoarseGrainedExecutorBackend.scala:    System.setProperty("spark.hostPort", sparkHostPort)
core/src/main/scala/org/apache/spark/executor/Executor.scala:    System.setProperty(key, value)
core/src/main/scala/org/apache/spark/executor/Executor.scala:    System.setProperty("spark.local.dir", getYarnLocalDirs())
core/src/main/scala/org/apache/spark/storage/StoragePerfTester.scala:    System.setProperty("spark.shuffle.compress", "false")
core/src/main/scala/org/apache/spark/storage/StoragePerfTester.scala:    System.setProperty("spark.shuffle.sync", "true")
core/src/main/scala/org/apache/spark/storage/ThreadingTest.scala:    System.setProperty("spark.kryoserializer.buffer.mb", "1")
core/src/main/scala/org/apache/spark/ui/UIWorkloadGenerator.scala:      System.setProperty("spark.scheduler.mode", "FAIR")
core/src/main/scala/org/apache/spark/util/MetadataCleaner.scala:    System.setProperty(MetadataCleanerType.systemProperty(cleanerType), delay.toString)
core/src/main/scala/org/apache/spark/util/MetadataCleaner.scala:    System.setProperty("spark.cleaner.ttl", delay.toString)
```

Shouldn't take too long to narrow down. Is that what you guys would prefer?