Add a sleep to prevent a failing test.

The BlockManager's put seems to be slightly asynchronous, which can
cause it to fail this test by not removing stuff from the cache before
we put the next value. We should probably change the semantics of put()
in this case but it's hard right now. It will also be hard for
asynchronously replicated puts.

core/src/test/scala/spark/storage/BlockManagerSuite.scala

@@ -215,6 +215,7 @@ class BlockManagerSuite extends FunSuite with BeforeAndAfterEach {
     assert(store.get("list3").get.size === 2)
     // Now let's add in list4, which uses both disk and memory; list1 should drop out
     store.put("list4", list4.iterator, StorageLevel.DISK_AND_MEMORY)
+    Thread.sleep(100)
     assert(store.get("list1") === None, "list1 was in store")
     assert(store.get("list2") != None, "list3 was not in store")
     assert(store.get("list2").get.size === 2)