tests: derive XglConstantBufferObj from xgl_testing::GpuMemory

Other than inheritance change, this also fixes two issues:
XGL_MEMORY_HEAP_CPU_VISIBLE_BIT was wrongly set when XGL_MEMORY_ALLOC_FLAGS is
expected.  xglWaitForFences was called with timeout==0 and is changed to
timeout==-1.
diff --git a/tests/xglrenderframework.h b/tests/xglrenderframework.h
index 9851bb9..1fd2e6c 100644
--- a/tests/xglrenderframework.h
+++ b/tests/xglrenderframework.h
@@ -132,23 +132,21 @@
 
 };
 
-class XglConstantBufferObj
+class XglConstantBufferObj : public xgl_testing::GpuMemory
 {
 public:
     XglConstantBufferObj(XglDevice *device);
     XglConstantBufferObj(XglDevice *device, int constantCount, int constantSize, const void* data);
-    ~XglConstantBufferObj();
     void SetMemoryState(XGL_MEMORY_STATE newState);
     void Bind(XGL_CMD_BUFFER cmdBuffer, XGL_GPU_SIZE offset, XGL_UINT binding);
     XGL_MEMORY_VIEW_ATTACH_INFO     m_constantBufferView;
-    XGL_GPU_MEMORY                  m_constantBufferMem;
 
 protected:
     XglDevice                      *m_device;
     int                             m_numVertices;
     int                             m_stride;
     XglCommandBufferObj             *m_commandBuffer;
-    XGL_FENCE                       m_fence;
+    xgl_testing::Fence              m_fence;
 };
 
 class XglIndexBufferObj : public XglConstantBufferObj