test: fix race condition

Join the generator thread in order to make sure it fully finished before
trying to read the values from it.

Signed-off-by: Jean-Louis Dupond <jean-louis@dupond.be>

Author: dupondje

client/src/test/java/org/ovirt/vdsm/jsonrpc/client/events/EventsThroughputTestCase.java

@@ -71,6 +71,10 @@ public void testThroughput() {
             Thread generator = new Thread(gen);
             generator.start();
             gen.stop(TIMEOUT);
+            try {
+                generator.join();
+            } catch (InterruptedException ignored) {
+            }
             unsubscribe();
         }
         System.out.println("Min value " + Collections.min(this.result));