Make DumpstateListener onError method oneway

The other change in this topic allows the onError
DumpstateListener call to be made asynchronous,
meaning that a blocking binder call will no longer be
made out of system_server.

Bug: 147703592
Test: Manual. Take bugreport, ensure that the death recipient
      logic never triggers before the onError/onFinished callback.
Change-Id: Ibb74bf068c4b186f07e19bb076b4ddea69eda768