Move BufferNode off ionbuffer

Because ionbuffer will be deprecated, and BufferNode is the server-side
memory management class for a BufferHubBuffer, we actually only need a
native_handle_t and AHardwareBuffer_Desc to keep the data.

Updated the test to check if buffer_handle_ is functioning correctly.

Test: atest buffer_node-test, buffer_hub-test
Fix: 117790952
Change-Id: Ie2c6814169d89e9c1ed5528442f2712abaf2ec8f