[java] copy the output in a daemon thread

Author: joerg1985

java/src/org/openqa/selenium/os/ExternalProcess.java

@@ -217,6 +217,7 @@ public ExternalProcess start() throws UncheckedIOException {
                 "External Process Output Forwarder - "
                     + (builder.command().isEmpty() ? "N/A" : builder.command().get(0)));
 
+        worker.setDaemon(true);
         worker.start();
 
         return new ExternalProcess(process, circular, worker);