Add a feature to get the last UpdateAttempt ErrorCode from update_engine

For autotest, update_engine test failures are always hard to debug,
since the error message is not clear. Add a new flag 'last_attempt_error'
to get the last UpdateAttempt ErrorCode from update_engine.

Bug:25598547
Test:emerge-peppy update_engine
     emerge-peppy update_engine_client
     cros flash a test image to DUT.
     (on the DUT):update_engine_client --last_attempt_error
     Compare the results with the update_engine logs, matched.

Change-Id: Id12681097ed30b0826cad68809f17f934a07e5b2
diff --git a/binder_service_brillo.cc b/binder_service_brillo.cc
index 45ac343..6a6a16e 100644
--- a/binder_service_brillo.cc
+++ b/binder_service_brillo.cc
@@ -186,6 +186,12 @@
   return Status::ok();
 }
 
+Status BinderUpdateEngineBrilloService::GetLastAttemptError(
+    int* out_last_attempt_error) {
+  return CallCommonHandler(&UpdateEngineService::GetLastAttemptError,
+                           out_last_attempt_error);
+}
+
 void BinderUpdateEngineBrilloService::UnregisterStatusCallback(
     IUpdateEngineStatusCallback* callback) {
   auto it = callbacks_.begin();