This fixes a bug where pre-0.9 executors fail to recover after an
upgrade.
The bug is that legacyExecutorWrappers didn't get updated with
ExecStreaming function, and thus failed to implement the Executor
function. Sadly, this meant that all recovery attempts fail, as the
runtime check in
b312aacbc9/drivers/shared/executor/utils.go (L103-L110)
.