syncbase/tests: close the test service properly

This change fixes a error that might happen during service clean up:
sync: processWatchLogBatch:: a, d: watcher cannot process batch:
nosql.test: Internal error: IO error:
/tmp/syncbase942811280/apps/a/d/leveldb/000007.ldb:
No such file or directory

Change-Id: I2a911fe749046eb32e2db143db60324e4723217f
diff --git a/services/syncbase/testutil/util.go b/services/syncbase/testutil/util.go
index 7af6f70..a3a8c72 100644
--- a/services/syncbase/testutil/util.go
+++ b/services/syncbase/testutil/util.go
@@ -249,7 +249,8 @@
 	name := s.Status().Endpoints[0].Name()
 	return name, func() {
 		cancel()
-		<-s.Closed()
+		s.Stop()
+		service.Close()
 		os.RemoveAll(rootDir)
 	}
 }