binderRpcTest: session leak test,time for shutdown

This is hard to reproduce locally, but it is happening on
our infrastructure as well as being reported by partners.

Bug: 275482320
Bug: 279834069
Test: binderRpcTest
Change-Id: I260e117092f7a181a3ad4358b2e5c416937d5295
diff --git a/libs/binder/tests/binderRpcTest.cpp b/libs/binder/tests/binderRpcTest.cpp
index 287e077..d01e9d7 100644
--- a/libs/binder/tests/binderRpcTest.cpp
+++ b/libs/binder/tests/binderRpcTest.cpp
@@ -687,6 +687,8 @@
     }
 
     EXPECT_EQ(nullptr, session.promote());
+
+    sleep(1); // give time for remote session to shutdown
 }
 
 TEST_P(BinderRpc, SingleDeathRecipient) {