message: sarkars/destructor order
  Free all executables before calling ReleaseBackend
diff: @@ -245,6 +245,10 @@ class NGraphEncapsulateOp : public OpKernel {
  }
  #endif
  + m_ng_exec_input_cache_map.clear();
  + m_ng_exec_output_cache_map.clear();
  + m_ng_exec_map.clear();
  + m_ng_function_map.clear();
  // Release the backend
  NGRAPH_VLOG(2) << "~NGraphEncapsulateOp():: ReleaseBackend";
  