Fix crash on exit

In RendererImpl::~RendererImpl, we have the following indirect call stack:

* teardownGlobalVkEmulation
* FrameBuffer::~FrameBuffer
* FrameBuffer::finalize
* RenderWindow::~RenderWindow
  Triggers FrameBuffer::finalize indirectly by sending the finalize
  command
* RendererImpl::~RendererImpl

However, teardownGlobalVkEmulation shouldn't be called until
mCleanupThread has exited, because we may have queued Vulkan objects
cleanups on that thread by calling
FrameBuffer::registerProcessCleanupCallback in on_vkCreateInstance, and
the clean up may depend on the global Vulkan emulation object.

Test: build
Change-Id: I667f2685dd9dc5749244844a3259e51a3250de7b

host/RendererImpl.cpp

diff --git a/host/RendererImpl.cpp b/host/RendererImpl.cpp
index bd224ef..c1fb7dd 100644
--- a/host/RendererImpl.cpp
+++ b/host/RendererImpl.cpp
@@ -184,6 +184,7 @@
     for (const auto& c : mStoppedChannels) {
         c->renderThread()->wait();
     }
+    mCleanupThread->waitForCleanup();
     mStoppedChannels.clear();
 }